Binder composition for additive manufacturing

ABSTRACT

Methods of additive manufacturing, binder compositions for additive manufacturing, and articles produced by and/or associated with methods of additive manufacturing are generally described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Application No. 62/890,871, filed Aug. 23, 2019, titled“Binder Compositions for Additive Manufacturing,” and U.S. ProvisionalApplication No. 62/924,093, filed Oct. 21, 2019, titled “BinderCompositions for Additive Manufacturing Comprising Low Molecular WeightPolymers Including Acrylic Acid Repeat Units,” each of which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

Methods of additive manufacturing, binder compositions for additivemanufacturing, and articles produced by and/or associated with methodsof additive manufacturing are generally described.

BACKGROUND

Additive manufacturing may be employed to form structures, such asthree-dimensional structures. Some methods of additive manufacturinginvolve employing a binder composition to adhere together a metalpowder. However, these methods of additive manufacturing typicallysuffer from a number of drawbacks. Examples of such drawbacks includeundesirable chemical interactions between the binder composition and themetal powder, poor mechanical integrity of metal-based composite objectsfabricated from the binder composition, limited shelf stability of thebinder composition, and/or the binder composition having a chemicalcomposition unsuitable for being deposited by a print head. Accordingly,improved methods of additive manufacturing, binder compositions foradditive manufacturing, and articles produced by and/or associated withmethods of additive manufacturing are needed.

SUMMARY

Methods of additive manufacturing, binder compositions for additivemanufacturing, and articles produced by and/or associated with methodsof additive manufacturing are generally described.

In some embodiments, a method of additive manufacturing a metal-basedcomposite structure by binder jet printing is provided. The methodcomprises depositing a first layer of metal powder, depositing a bindercomposition on at least a portion of the first layer of metal powder,and drying and/or cross-linking at least the binder compositiondeposited on the first layer of the metal powder, thereby forming ametal-based composite structure. The binder composition comprises waterand a low molecular weight polymer including an acrylic acid repeatunit. The binder composition has a pH of greater than or equal to 4.

In some embodiments, a method of additive manufacturing comprisesdepositing a first layer of metal powder, depositing a bindercomposition on at least a portion of the first layer of metal powder,drying and/or cross-linking at least the binder composition deposited onthe first layer of the metal powder, and heating the metal-basedcomposite structure in an environment having a temperature of greaterthan or equal to 700° C. and less than or equal to 1400° C. The bindercomposition comprises water and a low molecular weight polymer includingan acrylic acid repeat unit. The binder composition has a pH of greaterthan or equal to 4. Drying and/or cross-linking at least the bindercomposition deposited on the first layer of the metal powder results inthe formation of a metal-based composite structure.

In some embodiments, a binder composition for additive manufacturing ofmetal objects by binder jetting is provided. The binder compositioncomprises water, a low molecular weight polymer including an acrylicacid repeat unit, a cross-linking agent, and a pH modifier. Thecross-linking agent comprises a polyol, a multifunctional amine, and/ora multifunctional thiol.

In some embodiments, a three-dimensional composition formed by additivemanufacturing is provided. The three-dimensional composition comprises ametal powder and a binder composition. The binder composition compriseswater, a low molecular weight polymer including an acrylic acid repeatunit, a cross-linking agent, and a pH modifier. The cross-linking agentcomprises a polyol, a multifunctional amine, and/or a multifunctionalthiol.

In some embodiments, a metal-based composite structure formed byadditive manufacturing is provided. The metal-based composite structurecomprises a metal powder and a binder. The wt % of the metal powder inthe metal-based composite structure is between 92 wt % and 99.9 wt %.The binder comprises a low molecular weight polymer including an acrylicacid repeat unit.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 shows a non-limiting embodiment of a method of depositing a layerof metal powder, in accordance with some embodiments;

FIG. 2A shows a non-limiting embodiment of a method of depositing abinder composition onto at least a portion of a layer of metal powder,in accordance with some embodiments;

FIG. 2B shows a non-limiting embodiment of a method step of depositing asecond powder layer on a first powder layer onto which a bindercomposition had been deposited, in accordance with some embodiments;

FIG. 2C shows a non-limiting embodiment of a layer onto which a bindercomposition has been deposited, in accordance with some embodiments;

FIG. 3 shows one non-limiting embodiment of a method of drying and/orcross-linking a binder composition, in accordance with some embodiments;

FIG. 4 shows one non-limiting embodiment of a method of heating ametal-based composite structure, in accordance with some embodiments;

FIG. 5 shows one non-limiting embodiment of a method of heating ade-bound metal structure, in accordance with some embodiments;

FIGS. 6A-6B show two similar versions of an exemplary additivemanufacturing system, in accordance with some embodiments;

FIG. 7 shows one non-limiting embodiment of an additive manufacturingplant, in accordance with some embodiments;

FIG. 8A shows one non-limiting embodiment of a container configured toresist corrosion by a binder composition, in accordance with someembodiments;

FIG. 8B shows another non-limiting embodiment of a container configuredto resist corrosion by a binder composition, in accordance with someembodiments;

FIG. 8C shows one non-limiting example of an article for supplying abinder composition to an on-demand printing system;

FIG. 9A shows a non-limiting reaction scheme between a metal powder andan adhesion promoter, in accordance with some embodiments; and

FIG. 9B shows a non-limiting reaction scheme between a metal powder, anadhesion promoter, and a polymer, in accordance with some embodiments.

DETAILED DESCRIPTION

Methods of additive manufacturing, binder compositions for additivemanufacturing, and articles produced by and/or associated with methodsof additive manufacturing are generally described. Some of the methodsof additive manufacturing described herein employ a binder compositiondescribed herein having one or more advantageous features.

For instance, some binder compositions described herein have one or moreadvantages for use in combination with particular types of metalpowders. By way of example, in some embodiments, a binder composition asa whole is configured to interact with a metal powder such that themetal powder undergoes minimal amounts of deleterious chemicalreactions. For instance, a binder composition may have a pH that reducescorrosion of the relevant metal powder. In some embodiments, a binderincludes relatively low amounts of (or lacks) species that are highlyreactive with the metal powder and/or undesirably reactive with themetal powder. Binder compositions having this property may desirablyallow for the formation of metal-based composite structures and/or metalobjects in which the metal component(s) has a chemical composition closeto (or identical to) its composition in powder form and/or in which themetal powder has a desirable chemical composition.

As a second example, in some embodiments, a binder composition as awhole is configured to interact with a layer of metal powder such thatit penetrates the layer of metal powder and/or spreads within the layerof metal powder in a desirable manner. The binder composition may beconfigured to readily penetrate through the depth of the layer of metalpowder, which may assist with adhering the layer of metal powdertogether and/or may reduce the amount of undesired pores in ametal-based composite structure formed therefrom prior to sintering. Insome embodiments, a binder composition is configured to spread laterallyto a relatively low extent within a layer of metal powder. As excessivespreading is believed to cause the formation of metal objects that areoversized and/or rough, this property may assist with the formation ofmetal objects having fine features and/or that are smooth.

In some embodiments, a binder composition described herein is configuredto be compatible with one or more components of an additivemanufacturing system. By way of example, in some embodiments, a bindercomposition as a whole is configured to interact with one or morecomponents of the additive manufacturing system such that thecomponent(s) of the additive manufacturing system undergo minimalamounts of deleterious chemical reactions. For instance, a bindercomposition may have a pH that is non-corrosive to the component(s) ofthe additive manufacturing system, such as non-corrosive to the printhead of the additive manufacturing system (e.g., a print head comprisingsteel, such as a print head comprising a steel face plate). As anotherexample, in some embodiments, a binder composition as a whole has isconfigured such that it can be printed by an additive manufacturingsystem in a desirable manner. For instance, the binder composition as awhole may be configured to allow for the formation of droplets of adesired size and/or uniformity by a print head of the additivemanufacturing system. Such properties may allow for additivemanufacturing system to be capable of facilely printing the bindercomposition in a manner that results in the formation of desirablemetal-based composite structures without appreciable wear and tear ofthe on-demand printer.

In some embodiments, a binder composition described herein is configuredto be stored for an appreciable amount of time without undergoingundesirable transformations. For instance, in some embodiments, a bindercomposition described herein has a composition that retards and/orprevents the growth of biological contaminants therein. As anotherexample, a binder composition described herein may be provided in acontainer that is configured to resist degradation by the bindercomposition. These advantages may allow for some of the bindercompositions described herein to be prepared well in advance ofanticipated use and stored until needed.

It should be understood that some binder compositions described hereinmay have all of the above-described advantages, some binder compositionsdescribed herein may have a subset of the above-described advantages,and binder compositions described herein may have none of theabove-described advantages. Similarly, some binder compositionsdescribed herein may have advantages not described above and/or may bedesirable for use in a variety of applications for reasons not describedabove. Particular features of binder compositions that may promote oneor more of the above-described advantages are described in furtherdetail below.

Some embodiments relate methods of additive manufacturing, bindercompositions for additive manufacturing, and/or articles formed byadditive manufacturing (e.g., three-dimensional compositions,metal-based composite structures, metal objects). For instance, a bindercomposition having one or more of the advantageous properties describedherein may be employed in a method of additive manufacturing describedherein to form a three-dimensional composition, metal-based compositestructure, and/or metal object described herein. An overview of stepsthat may be included in methods of additive manufacturing is providedbelow. It should be understood that some methods of additivemanufacturing may comprise some of the steps described below but lackover the steps described below, that some methods of additivemanufacturing may comprise all of the steps described below, that somemethods of additive manufacturing may comprise none of the stepsdescribed below, and that some methods of additive manufacturing maycomprise further steps not described below.

In some embodiments, a method of additive manufacturing comprises a stepof depositing a layer of metal powder. This step may comprise dispersinga metal powder to form a layer thereof. The metal powder may initiallynot be in the form of layer (e.g., it may be in the form of a source ofmetal powder enclosed in a container, in the form of a pile, etc.). FIG.1 shows one non-limiting embodiment of a method of depositing a layer ofmetal powder in which a metal powder 10 is deposited to form a layer ofmetal powder 20. In some embodiments, a metal powder is deposited toform the layer thereof by one or more tools, non-limiting examples ofwhich include rollers, doctor blades, and sifters. Depositing a metalpowder to form a layer thereof is typically performed such that theresultant layer of metal powder is formed on a substrate. Appropriateexamples of substrates include bases on which the article formed by theadditive manufacturing method is designed to be formed (e.g., platformscomprising metals and/or ceramics, sheets comprising metals and/orceramics) and layers disposed on such bases (e.g., one or more layers ofmetal powder disposed on a base on which the article formed by theadditive manufacturing method is designed to be formed, one or morelayers formed in an additive manufacturing process, such as one or moreof the layers formed by one or more of the processes described below).Layers disposed on such bases may include layer(s) configured to beincorporated into an article formed by additive manufacturing (e.g., inthe case of layer(s) themselves formed by additive manufacturing and/orlayer(s) not configured to be incorporated into an article formed byadditive manufacturing (e.g., in the case of layer(s) of metal powder).

In some embodiments, the deposited metal powder comprises a preciousmetal. It should be understood that in the context of this disclosure,when a metal powder is said to comprise a precious metal, differentconfigurations are possible. For example, the metal powder may comprisea mixture of different types of particles, some of which contain theprecious metal, some of which do not. As a specific example, a metalpowder comprising gold metal may comprise a mixture of goldmetal-containing particles and non-gold-metal-containing particles(e.g., particles made entirely of zinc metal). The particles containingthe precious metal may be formed entirely of the precious metal in someinstances, while in other instances the particles containing theprecious metal may comprises a mixture (e.g., alloy) or composite of theprecious metal and one or more other components such as other metals(e.g., gold alloyed with zinc). In some embodiments, the precious-metalcontaining particles of a metal powder each comprises the precious metalin an amount of greater than or equal to 10 wt %, greater than or equalto 25 wt %, greater than or equal to 50 wt %, greater than or equal to75 wt %, greater than or equal to 90 wt %, and/or up to 92.5 wt %, up to95 wt %, up to 98 wt %, up to 99 wt %, up to 99.9 wt %, or 100 wt %(understanding that the precious-metal particles may not necessarilyeach contain the same amount of the precious metal). In someembodiments, a metal powder comprising a precious metal comprisesparticles, each of which comprises the precious metal. As describedabove, in such embodiments, these precious metal-containing particlesmay each be made entirely of the precious metal, or some or all of theprecious metal-containing particles may contain a mixture (e.g., alloy)or composite of the precious metal and one or more other components (theparticles each having the same amount of precious metal in someinstances, and the particles having differing amounts of the preciousmetal in other instances).

Certain method steps and/or binder compositions described herein mayhelp overcome challenges associated with additive manufacturing withprecious metal using existing techniques and binders, such as pooradhesion between certain binder components and the metal. Referringagain to FIG. 1, metal powder 10, which is deposited to form a layer ofmetal powder 20, is or comprises a precious metal powder (e.g., a powdercomprising one or more precious metals), according to some embodiments.As used herein, “precious metals” may refer at least to ruthenium (Ru),rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir),platinum (Pt), gold (Au), or combinations thereof. In certain instancesin which the metal powder comprises a precious metal powder, theprecious metal powder comprises silver metal and/or a silver alloy. Inan exemplary embodiment, the precious metal powder comprises sterlingsilver. Sterling silver generally refers to a silver alloy having asilver content of greater than or equal to 92.5 weight percent (wt %).Sterling silver may contain silver alloyed with copper (e.g., at 7.5 wt%) to improve properties such as hardness and strength, though in somecases other elements such as germanium (Ge) are used). In someembodiments, the precious metal powder comprises platinum and/or aplatinum alloy (e.g., platinum alloyed with cobalt (Co), ruthenium,and/or iridium). In some instances, the precious metal powder comprisesgold metal and/or a gold alloy (e.g., gold alloyed with zinc (Zn),copper, silver, nickel (Ni), iron (Fe), cadmium (Cd), aluminum (Al),and/or palladium (Pd)). In some instances, the precious metal powdercomprises platinum metal and/or a platinum alloy (e.g., platinum alloyedwith iridium, ruthenium, palladium, cobalt, and/or copper (Cu)). Themetal powder may have only a single precious metal present, though insome embodiments the metal powder comprises two or more precious metals.As one non-limiting example, the metal powder may comprise a mixture ofsilver metal powder and gold metal powder. In some embodiments in whichthe metal powder comprises a metal alloy (e.g., a precious metal alloysuch as sterling silver), the metal powder comprises a plurality ofparticles of the metal alloy (e.g., a plurality of sterling silverparticles).

The metal powder may have a relatively high content of the preciousmetal and/or precious metal alloy, by weight. Having a relatively highcontent of precious metal, and/or precious metal alloy in the metalpowder may result in the manufacture of a metal-based compositestructure and/or a completed metal object having a relatively highprecious metal content during or following the additive manufacturingprocess. In some embodiments, the precious metal (e.g., gold, silver,platinum) or precious metal alloy (e.g., rose gold, sterling silver) ispresent in the metal powder in an amount of greater than or equal to 25wt %, greater than or equal to 30 wt %, greater than or equal to 40 wt%, greater than or equal to 50 wt %, greater than or equal to 60 wt %,greater than or equal to 65 wt %, greater than or equal to greater thanor equal to 70 wt %, greater than or equal 75 wt %, greater than orequal to 80 wt %, greater than or equal to 85 wt %, greater than orequal to 90 wt %, greater than or equal to 91 wt %, greater than orequal to 92 wt %, greater than or equal to 92.5 wt %, greater than orequal to 93 wt %, greater than or equal to 93.5 wt %, greater than orequal to 94%, greater than or equal to 94.5 wt %, greater than or equalto 95 wt %, greater than or equal to 95.5 wt %, greater than or equal to96 wt %, greater than or equal to 96.5 wt %, greater than or equal to 97wt %, greater than or equal to 97.5 wt %, greater than or equal to 98 wt%, greater than or equal to 98.5 wt %, greater than or equal to 99 wt %,greater than or equal to 99.5 wt %, greater than or equal to 99.7 wt %,greater than or equal to 99.8 wt %, or greater than or equal to 99.9 wt%. The precious metal (e.g., gold, silver, platinum), precious metalalloy (e.g., rose gold, sterling silver) may be present in the metalpowder in amount of less than or equal to substantially 100 wt %, lessthan or equal to 99.9 wt %, less than or equal to 99.8 wt %, less thanor equal to 99.7 wt %, less than or equal to 99.5 wt %, less than orequal to 99 wt %, less than or equal to 98.5 wt %, less than or equal to98 wt %, less than or equal to 97.5 wt %, less than or equal to 97 wt %,less than or equal to 96.5 wt %, less than or equal to 96 wt %, lessthan or equal to 95.5 wt %, less than or equal to 96 wt %, less than orequal to 95.5 wt %, less than or equal to 95 wt %, less than or equal to94.5 wt %, less than or equal to 94 wt %, less than or equal to 93.5 wt%, less than or equal to 93 wt %, less than or equal to 92.5 wt %, lessthan or equal to 92 wt %, less than or equal to 91 wt %, less than orequal to 90 wt %, less than or equal to 85 wt %, less than or equal to80 wt %, less than or equal to 75 wt %, less than or equal to 70 wt %,less than or equal to 65 wt %, less than or equal to 60 wt %, less thanor equal to 50 wt %, less than or equal to 40 wt %, or less.Combinations of these ranges are possible (e.g., greater than or equalto 25 wt % and less than or equal to substantially 100 wt %, greaterthan or equal to 25 wt % and less than or equal to 99.9 wt %, or greaterthan or equal to 92.5 wt % and less than or equal to 99.9 wt %). Otherranges are possible.

For example, in some embodiments, the metal powder comprises gold metaland/or a gold alloy in certain of the ranges described above. In someembodiments, gold is present in the metal powder in an amount of greaterthan or equal to 25 wt %, greater than or equal to greater than or equalto 30 wt %, greater than or equal to 40 wt %, greater than or equal to50 wt %, greater than or equal to 60 wt %, greater than or equal to 65wt %, greater than or equal to greater than or equal to 70 wt %, greaterthan or equal 75 wt %, greater than or equal to 80 wt %, greater than orequal to 85 wt %, greater than or equal to 90 wt %, greater than orequal to 91 wt %, greater than or equal to 92 wt %, greater than orequal to 92.5 wt %, greater than or equal to 93 wt %, greater than orequal to 93.5 wt %, greater than or equal to 94%, greater than or equalto 94.5 wt %, greater than or equal to 95 wt %, greater than or equal to95.5 wt %, greater than or equal to 96 wt %, greater than or equal to96.5 wt %, greater than or equal to 97 wt %, greater than or equal to97.5 wt %, greater than or equal to 98 wt %, greater than or equal to98.5 wt %, greater than or equal to 99 wt %, greater than or equal to99.5 wt %, greater than or equal to 99.7 wt %, greater than or equal to99.8 wt %, or greater than or equal to 99.9 wt %. Gold metal may bepresent in the metal powder in amount of less than or equal tosubstantially 100 wt %, less than or equal to 99.9 wt %, less than orequal to 99.8 wt %, less than or equal to 99.7 wt %, less than or equalto 99.5 wt %, less than or equal to 99 wt %, less than or equal to 98.5wt %, less than or equal to 98 wt %, less than or equal to 97.5 wt %,less than or equal to 97 wt %, less than or equal to 96.5 wt %, lessthan or equal to 96 wt %, less than or equal to 95.5 wt %, less than orequal to 96 wt %, less than or equal to 95.5 wt %, less than or equal to95 wt %, less than or equal to 94.5 wt %, less than or equal to 94 wt %,less than or equal to 93.5 wt %, less than or equal to 93 wt %, lessthan or equal to 92.5 wt %, less than or equal to 92 wt %, less than orequal to 91 wt %, less than or equal to 90 wt %, less than or equal to85 wt %, less than or equal to 80 wt %, less than or equal to 75 wt %,less than or equal to 70 wt %, less than or equal to 65 wt %, less thanor equal to 60 wt %, less than or equal to 50 wt %, less than or equalto 40 wt %, or less. Combinations of these ranges are possible (e.g.,greater than or equal to 25 wt % and less than or equal to substantially100 wt %, greater than or equal to 25 wt % and less than or equal to99.9 wt %, or greater than or equal to 92.5 wt % and less than or equalto 99.9 wt %). Other ranges are possible. It should be understood thatthe amount of gold metal in a material may also be expressed in terms ofkarat. An alloy having gold present in an amount of 100 wt % (pure gold)has 24 karats. Therefore, an alloy having gold present in an amount of75 wt % has 18 karat, an alloy having gold present in an amount of 50 wt% has 12 karats, and so forth. In some embodiments, the metal powder isa gold alloy powder having greater than or equal to 6 karats, greaterthan or equal to 8 karats, greater than or equal to 12 karats, greaterthan or equal to 14 karats, greater than or equal to 16 karats, greaterthan or equal to 18 karats, greater than or equal to 20 karats, greaterthan or equal to 22 karats, greater than or equal to 23 karats, or more.In some embodiments, the metal powder is a gold alloy powder having lessthan or equal to 24 karats, less than or equal to 23 karats, less thanor equal to 22 karats, less than or equal to 21 karats, less than orequal to 20 karats, less than or equal to 18 karats, less than or equalto 16 karats, less than or equal to 14 karats, less than or equal to 12karats, less than or equal to 10 karats, less than or equal to 8 karats,or less. Combinations (e.g., greater than or equal to 6 karats and lessthan or equal to 24 karats) are possible. Other ranges are alsopossible. Various gold alloys are possible. Non-limiting examples ofgold alloys include yellow gold (e.g., 75 wt % gold, 16 wt % silver, 9wt % copper) and rose gold (e.g., 75 wt % gold, 6 wt % silver, 19 wt %copper).

In some embodiments, the metal powder comprises silver metal and/or asilver alloy in certain of the ranges described above. In someembodiments, silver is present in the metal powder in an amount ofgreater than or equal to 90 wt %, greater than or equal to 91 wt %,greater than or equal to 92 wt %, greater than or equal to 92.5 wt %,greater than or equal to 93 wt %, greater than or equal to 93.5 wt %,greater than or equal to 94%, greater than or equal to 94.5 wt %,greater than or equal to 95 wt %, greater than or equal to 95.5 wt %,greater than or equal to 96 wt %, greater than or equal to 96.5 wt %,greater than or equal to 97 wt %, greater than or equal to 97.5 wt %,greater than or equal to 98 wt %, greater than or equal to 98.5 wt %,greater than or equal to 99 wt %, greater than or equal to 99.5 wt %,greater than or equal to 99.7 wt %, greater than or equal to 99.8 wt %,or greater than or equal to 99.9 wt %. In some embodiments, silver ispresent in the metal powder in an amount of less than or equal tosubstantially 100 wt %, less than or equal to 99.9 wt %, less than orequal to 99.8 wt %, less than or equal to 99.7 wt %, less than or equalto 99.5 wt %, less than or equal to 99 wt %, less than or equal to 98.5wt %, less than or equal to 98 wt %, less than or equal to 97.5 wt %,less than or equal to 97 wt %, less than or equal to 96.5 wt %, lessthan or equal to 96 wt %, less than or equal to 95.5 wt %, less than orequal to 96 wt %, less than or equal to 95.5 wt %, less than or equal to95 wt %, less than or equal to 94.5 wt %, less than or equal to 94 wt %,less than or equal to 93.5 wt %, less than or equal to 93 wt %, lessthan or equal to 92.5 wt %, less than or equal to 92 wt %, less than orequal to 91 wt %, or less. Combinations (e.g., greater than or equal to90 wt % and less than or equal to 100 wt %, or greater than or equal to92.5 wt % and less than or equal to 100 wt %) are possible. Other rangesfor the amount of silver in the metal powder are also possible. Varioussilver alloys are possible. Non-limiting examples of silver alloysinclude sterling silver and argentium silver (e.g., 93.5 wt % or 96 wt %silver alloyed with other metals or metalloids, such as germanium).

In some embodiments, the metal powder comprises platinum metal and/or aplatinum alloy in certain of the ranges described above. In someembodiments, platinum is present in the metal powder in an amount ofgreater than or equal to 90 wt %, greater than or equal to 91 wt %,greater than or equal to 92 wt %, greater than or equal to 92.5 wt %,greater than or equal to 93 wt %, greater than or equal to 93.5 wt %,greater than or equal to 94%, greater than or equal to 94.5 wt %,greater than or equal to 95 wt %, greater than or equal to 95.5 wt %,greater than or equal to 96 wt %, greater than or equal to 96.5 wt %,greater than or equal to 97 wt %, greater than or equal to 97.5 wt %,greater than or equal to 98 wt %, greater than or equal to 98.5 wt %,greater than or equal to 99 wt %, greater than or equal to 99.5 wt %,greater than or equal to 99.7 wt %, greater than or equal to 99.8 wt %,or greater than or equal to 99.9 wt %. In some embodiments, platinum ispresent in the metal powder in an amount of less than or equal tosubstantially 100 wt %, less than or equal to 99.9 wt %, less than orequal to 99.8 wt %, less than or equal to 99.7 wt %, less than or equalto 99.5 wt %, less than or equal to 99 wt %, less than or equal to 98.5wt %, less than or equal to 98 wt %, less than or equal to 97.5 wt %,less than or equal to 97 wt %, less than or equal to 96.5 wt %, lessthan or equal to 96 wt %, less than or equal to 95.5 wt %, less than orequal to 96 wt %, less than or equal to 95.5 wt %, less than or equal to95 wt %, less than or equal to 94.5 wt %, less than or equal to 94 wt %,less than or equal to 93.5 wt %, less than or equal to 93 wt %, lessthan or equal to 92.5 wt %, less than or equal to 92 wt %, less than orequal to 91 wt %, or less. Combinations (e.g., greater than or equal to90 wt % and less than or equal to 100 wt %, or greater than or equal to92.5 wt % and less than or equal to 100 wt %) are possible. Other rangesfor the amount of platinum in the metal powder are also possible.Various platinum alloys are possible. For example the metal powder maycomprise an alloy of platinum and iridium (e.g., Pt950/Ir containing 95wt % Pt and 5 wt % Jr, Pt900/Ir containing 90 wt % Pt and 10 wt % Jr, orPt850/Ir containing 85 wt % Pt and 15 wt % Jr). As another example, themetal powder may comprise an alloy of platinum and ruthenium (e.g.,Pt950/Ru containing 95 wt % Pt and 5 wt % Ru). As yet another example,the metal powder may comprise an alloy of platinum and palladium (e.g.,Pt950/Pd containing 95 wt % Pt and 5 wt % Pd). As yet another example,the metal powder may comprise an alloy of platinum and cobalt (e.g.,Pt950/Co containing 95 wt % Pt and 5 wt % Co). As yet another example,the metal powder may comprise an alloy of platinum and copper (e.g.,Pt960/Cu containing 96 wt % Pt and 4 wt % Cu). In some embodiments, themetal powder comprises an alloy of platinum, cobalt, and palladium(e.g., Pt850/Co50/Pd100 containing 85 wt % Pt, 5 wt % Co, and 10 wt %Pd).

Once a layer of metal powder is obtained, a method of additivemanufacturing may comprise depositing a binder composition onto at leasta portion of the layer of metal powder. FIG. 2A shows one example ofthis method step, as it depicts the deposition of a binder composition100 on a layer 200 of metal powder. The metal powder comprises aplurality 210 of metal particles. In some embodiments, like theembodiment shown in FIG. 2A, the binder composition may be deposited onthe metal powder in the form of droplets, such as in the form of aplurality of droplets formed by a print head. By way of example, amethod of additive manufacturing described herein may compriseperforming a binder jet printing process.

An additive manufacturing method may comprise performing the steps shownin FIGS. 1 and 2A multiple times successively. For instance, a method ofadditive manufacturing may comprise depositing a first layer of metalpowder, then depositing a binder composition on at least a portion ofthe first layer of metal powder, and then depositing a second layer ofmetal powder on the first layer of metal powder. As another example, amethod of additive manufacturing may comprise depositing a bindercomposition on at least a portion of a first layer of metal powder, thendepositing a second layer of metal powder on the first layer of metalpowder, and then depositing a binder composition on at least a portionof the second layer of metal powder. It can be seen that some methods ofadditive manufacturing may comprise performing these two steps in analternating manner at least twice, at least three times, at least fourtimes, at least five times, at least ten times, at least a hundredtimes, or a number of times sufficient to build up a metal-basedcomposite structure.

Methods comprising performing successive steps of depositing a layer ofmetal powder and depositing a binder composition onto at least a portionof the layer of metal powder may be performed in a variety of manners.By way of example, FIG. 2B shows a method step of depositing a secondpowder layer 252 on the first powder layer onto which a bindercomposition had been deposited.

In some embodiments, the sequential steps of depositing a layer of metalpowder and depositing a binder composition thereon may be performed in amanner in which the binder deposited on at least a portion of a firstlayer of metal powder is not dried or cross-linked prior to depositing asecond layer of metal powder on the first layer of metal powder (e.g.,the second layer of metal powder is deposited on the first layer ofmetal powder prior to drying or cross-linking the binder composition).The article formed by such successive steps may be referred to elsewhereherein as a “three-dimensional composition”. In some embodiments, thesequential steps of depositing a layer of metal powder and depositing abinder composition thereon may be performed in a manner in which thebinder deposited on at least a portion of a first layer of metal powderis dried and/or cross-linked prior to depositing a second layer of metalpowder on the first layer of metal powder.

It should be noted that some embodiments may comprise both of theabove-referenced sequences of steps. For instance, the steps ofsequentially depositing a layer of metal powder and then depositing abinder composition onto at least a portion of the layer of metal powdermay be repeated a number of times without performing any drying orheating process on the binder composition (e.g., one or more layers ofmetal powder may be deposited prior to cross-linking or drying thebinder composition previously deposited, binder composition may bedeposited onto at least a portion of a layer of metal powder depositedprior to the cross-linking or drying of the binder compositionpreviously deposited). These steps may result in the formation of athree-dimensional composition. Then, the binder composition may be driedand/or cross-linked to form a metal-based composite structure from thethree-dimensional composition. After which, further steps ofsequentially depositing a layer of metal powder and then depositing abinder composition onto at least a portion of the layer of metal powdermay be performed thereon. The second three-dimensional composition mayalso be dried and/or cross-linked. This drying and/or cross-linking mayresult in the formation of a new metal-based composite structurecomprising the prior metal-based composite structure and the driedand/or cross-linked three-dimensional composition formed thereon.

In some embodiments, a step of depositing a binder composition on atleast a portion of a layer of metal powder like that shown in FIG. 2A orFIG. 2B comprises depositing a binder composition on a layer of metalpowder such that it contacts some portions of the layer of metal powderand does not contact other portions of the layer of metal powder. Thebinder composition may penetrate into and/or spread into portions of thelayer of metal powder that it contacts and may not penetrate or spreadinto portions of the layer of metal powder that it does not contact.This process may result in the formation of a layer having a morphologylike that shown in FIG. 2C. In FIG. 2C, a layer 304 comprises a portion354 comprising both a binder composition and a portion of the layer ofmetal powder and a portion 364 comprising a portion of the layer ofmetal powder but lacking the binder composition. The portions of thelayer of metal powder through which the binder composition haspenetrated and/or spread may be adhered together by one or morecomponents of the binder composition (e.g., a polymer) upon depositionthereof and/or during later processing steps. The portions of the layerof metal powder through which the binder composition has not penetratedor spread may remain unadhered to each other.

During formation of a three-dimensional composition, deposition of abinder composition on a layer or metal powder may also comprisedepositing a portion of the binder composition onto layer positionedtherebeneath. Advantageously, this may adhere together layers in thethree-dimensional composition with the layers to which they are directlyadjacent, which may result in the formation of a three-dimensionalobject, metal-based composite structure, or combination of metal-basedcomposite structures adhered together in all three dimensions and/orhaving a continuous morphology.

As described above, some methods of additive manufacturing compriseforming a metal-based composite structure (e.g., from a layer comprisinga binder composition, from a three-dimensional composition) (e.g., in aprocess comprising drying and/or cross-linking a binder composition). Asalso described above, the binder composition may be a binder compositionpresent in a three-dimensional composition and/or may be a bindercomposition present in a layer disposed on a metal-based compositestructure.

Drying the binder composition may comprise exposing the bindercomposition to a stimulus that causes one or more volatile componentstherein to evaporate (e.g., free water, organic solvents, volatile pHmodifiers). Other, non-volatile and/or less volatile components of thebinder composition may not be removed by a drying process (e.g., boundwater, a polymer, a cross-linking agent).

Cross-linking the binder composition may comprise exposing the bindercomposition to a stimulus that causes one or more portions thereof toundergo a cross-linking reaction (e.g., a polymer, a cross-linkingagent). Non-limiting examples of suitable stimuli include heat and light(e.g., microwave radiation, UV light), wherein heat transfer may includeany combination of conduction, convection and/or radiation. Convectiveheat transfer may include, but is not limited to, forced convectionthrough the powder bed. Heat and/or light stimuli may be suitable bothfor drying the binder composition and cross-linking the bindercomposition; other such stimuli may only be suitable for one or theother. In some embodiments, a binder composition may be dried and thencross-linked. The drying step may comprise removing one or morecomponents that would interfere with the cross-linking step. Forinstance, a drying step may comprise removing water (e.g., water thatcauses the equilibrium of the cross-linking reaction to favor breakingcross-links instead of forming cross-links) and/or may comprise removinga pH modifier (e.g., a pH modifier that would interfere with thecross-linking reaction).

FIG. 3 shows one example of a step of drying and/or cross-linking abinder composition, in which a stimulus is applied to a layer 306 toform a metal-based composite structure 406. In some embodiments, amethod like that shown in FIG. 3 is performed on a single layercomprising a layer of metal particles and a binder (and/or a layer ofmetal particles on which a binder is disposed). In some embodiments, amethod like that shown in FIG. 3 is performed on a series of such layersdisposed on each other in a three-dimensional compositionsimultaneously.

In some embodiments, a metal-based composite structure may undergo oneor more further steps. By way of example, portion(s) of a layer of metalpowder (and/or layers of metal powder forming a metal powder bed) ontowhich the binder has been deposited may be incorporated into themetal-based composite structure while other portion(s) (e.g., portionsonto which the binder composition was not deposited) may not beincorporated into the metal-based composite structure. One or moreportion(s) of the layer(s) of metal powder and/or metal powder bed notincorporated into the metal-based composite structure may be removedtherefrom. This may be accomplished by, for example, removing themetal-based composite structure from a powder bed.

As another example, a metal-based composite structure may be heated. Theheating may comprise positioning the metal-based composite structure inan environment at a temperature that results in the removal of one ormore components of the binder composition previously retained in thecomposite structure. For instance, the heating may remove a polymer fromthe binder composition retained in the composite structure and/or one ormore other components of the binder composition not removed from thecomposite structure by prior drying and/or cross-linking steps. In someembodiments, heating the composite structure may cause thermaldecomposition of these components of the binder composition that arethen volatilized or retained as solids (e.g., as char) positioned withinthe resultant structure. The resultant structure may also be referred toherein as a “de-bound metal structure”. FIG. 4 shows one example of aheating step, in which heat is applied to a metal-based compositestructure 408 to form a de-bound metal structure 608. During a heatingstep, the particles present in the metal-based composite structure mayadhere together directly as the portion(s) of the binder composition arebeing removed.

In some embodiments, a metal-based composite structure and/or a de-boundmetal structure undergoes a heating step to form a metal object. Thisheating step may comprise heating an environment in which themetal-based composite structure and/or de-bound metal structure ispositioned to a temperature that allows for diffusion of metalcomponents within the metal-based composite structure and/or de-boundmetal structure but that does not melt the metal-based compositestructure and/or de-bound metal structure to an undesirable extent. Forexample, this heating step may comprise heating the environment to atemperature that promotes sintering of the metal-based compositestructure and/or de-bound metal structure. Advantageously, diffusionthat occurs during sintering may further bond together the resultantmetal object and/or may reduce (and/or eliminate) any porosity presentin the metal-based composite structure and/or de-bound metal structure.This diffusion may also cause the metal-based composite structure and/orde-bound metal structure to densify, which may enhance its surfacefinish, mechanical properties, and/or electrical conductivity. FIG. 5shows one example of a step of heating a de-bound metal structure, inwhich heat is applied to a de-bound metal structure 610 to form a metalobject 710.

In some embodiments, one or more of the method steps described above maybe performed in an additive manufacturing system. FIGS. 6A and 6B showtwo similar versions of an exemplary additive manufacturing system 1100.The various components of this additive manufacturing system and itsoperation are described below.

The additive manufacturing system 1100 shown in FIGS. 6A and 6B may beused to form an article 1102 from a metal powder 1104. The article 1102may be a three-dimensional composition as described elsewhere herein.For instance, it may comprise a binder composition and a metal powdercomprising a plurality of metal particles (e.g., as shown in FIGS.2A-2C). As also described elsewhere herein, the three-dimensionalcomposition 1102 can undergo subsequent steps to form a metal object.While the additive manufacturing system shown in FIGS. 6A and 6B issuitable for performing a binder jetting process to form athree-dimensional composition (e.g., by selectively joining portions oflayers of metal powder with a binder composition in a sequentialmanner), it should be understood that the current disclosure is notlimited to any particular type of additive manufacturing process orpowder process (e.g., any particular type of powder metallurgicalprocess) involving a binder. For example, other suitable processes thatmay be employed to form a three-dimensional composition to form athree-dimensional composition include, but are not limited to injectionmolding processes and powder fusion processes (e.g., selective lasermelting processes).

The additive manufacturing system 1100 shown in FIGS. 6A and 6B caninclude a powder deposition mechanism 1106 (e.g., shown in FIG. 6B) anda print head (e.g., shown as print head 1118 in FIG. 6A and print head1108 in FIG. 6B), which may be coupled to and moved across the printarea by a unit 1107 (e.g., as shown in FIG. 6B). The powder depositionmechanism 1106 may be operated to deposit a layer of metal powder bydepositing powder 1104 onto the powder bed 1114.

In some embodiments, a powder deposition mechanism comprises a metalpowder supply 1112, a metal powder bed 1114, and a spreader 1116 (e.g.,as shown in FIG. 6A). When present, the spreader 1116 can be movablefrom the metal powder supply 1112 to the metal powder bed 1114 and alongthe metal powder bed 1114 to deposit a metal powder onto the metalpowder bed 1114 and to deposit successive layers of the metal powderacross the metal powder bed 1114. As discussed in more detail below, theadditive manufacturing apparatus 1100 and/or the spreader 1116 thereinmay be configured to deposit layers of metal powder on the powder bedhaving any suitable geometry (e.g., layers of metal powder having ahomogeneous, planar geometry; layers of metal powder having a morphologyother than a homogeneous, planar geometry). Depending on the particularembodiment, the spreader 1116 may include, for example, a rollerrotatable about an axis perpendicular to an axis of movement of thespreader 1116 across the powder bed 1114. The roller can be, forexample, substantially cylindrical. In use, rotation of the roller aboutthe axis perpendicular to the axis of movement of the spreader 1116 candeposit the metal powder from the metal powder supply 1112 to the metalpowder bed 1114 and form a layer of the metal powder along the metalpowder bed 1114. It should be appreciated, therefore, that a pluralityof sequential layers of the material 1104 can be formed in the metalpowder bed 1114 through repeated movement of the spreader 1116 acrossthe metal powder bed 1114.

The print head 1108 (in FIG. 6B) and/or 1118 (in FIG. 6A) can be movable(e.g., in coordination with movement of the spreader 1116) across themetal powder bed 1114 and/or can be stationary (e.g., in embodiments inwhich the platform 1105 is movable). In some embodiments, the print head1108 and/or 1118 includes one or more orifices through which a liquid(e.g., a binder composition) can be delivered from the print head 1118to each layer of the metal powder along the metal powder bed 1114. Incertain embodiments, the print head 1108 and/or 1118 can include one ormore piezoelectric elements, and each piezoelectric element may beassociated with a respective orifice and, in use, each piezoelectricelement can be selectively actuated such that displacement of thepiezoelectric element can expel liquid from the respective orifice. Insome embodiments, the print head 1108 and/or 1118 may be arranged toexpel a single liquid formulation from the one or more orifices. Inother embodiments, the print head 1108 and/or 1118 may be arranged toexpel a plurality of liquid formulations from the one or more orifices.For example, the print head 1108 and/or 1118 can expel a plurality ofliquids (e.g., a plurality of solvents), a plurality of components of abinder composition, or both from the one or more orifices. Moreover, insome instances, expelling or otherwise delivering a liquid from theprint head may include emitting an aerosolized liquid (i.e., an aerosolspray) from a nozzle of the print head.

In general, the print head 1108 in FIG. 6B and/or 1118 in FIG. 6A may becontrolled to deliver liquid such as a binder composition to the metalpowder bed 1114 in predetermined two-dimensional patterns, with eachpattern corresponding to a respective layer of the three-dimensionalcomposition 1102. In this manner, the delivery of the binder compositionmay be a printing operation in which the metal powder in each respectivelayer of the three-dimensional composition is selectively joined alongthe predetermined two-dimensional layers. After each layer of thethree-dimensional composition is formed as described above, the platform1105 may be moved down and a new layer of metal powder deposited, bindercomposition again applied to the new metal powder, etc. until the objecthas been formed.

In some embodiments, the print head 1108 (in FIG. 6B) and/or 1118 (inFIG. 6A) can extend axially along substantially an entire dimension ofthe metal powder bed 1114 in a direction perpendicular to a direction ofmovement of the print head 1108 and/or 1118 across the metal powder bed1114. For example, in such embodiments, the print head 1118 can define aplurality of orifices arranged along the axial extent of the print head1108 and/or 1118, and liquid can be selectively jetted from theseorifices along the axial extent to form a predetermined two-dimensionalpattern of liquid along the metal powder bed 1114 as the print head 1108and/or 1118 moves across the metal powder bed 1114. In some embodiments,the print head 1108 and/or 1118 may extend only partially across themetal powder bed 1114, and the print head 1108 and/or 1118 may bemovable in two dimensions relative to a plane defined by the powder bed1114 to deliver a predetermined two-dimensional pattern of a liquidalong the powder bed 1114.

The additive manufacturing system 1100 generally further includes acontroller 1120 in electrical communication with one or more othersystem components. For instance, in FIG. 6A, a controller 1120 is inelectrical communication with the metal powder supply 1112, the metalpowder bed 1114, the spreader 1116, and the print head 1118. In FIG. 6B,the controller 1120 is in electrical communication with the unit 1107,the powder deposition mechanism 1106, and the print head 1108. Also inFIG. 6B, the controller 1120 may be configured to control the motion ofthe unit 1107, the material deposition mechanism 1106, and the printhead 1108 as described above.

A non-transitory, computer readable storage medium 1122 may be incommunication with the controller 1120 and have stored thereon athree-dimensional model 1124 and instructions for carrying out any oneor more of the methods described herein. Alternatively, thenon-transitory, computer readable storage medium may comprise previouslyprepared instructions. With reference to FIG. 6B, such instructions,when executed by the controller 1120, may operate the platform 1105, theunit 1107, the material deposition mechanism 1106, and the print head1108 to fabricate one or more three-dimensional compositions. Forexample, one or more processors of the controller 1120 can executeinstructions to move the unit 1107 forwards and backwards along anx-axis direction across the surface of the powder bed 1114. One or moreprocessors of the controller 1120 also may control the materialdeposition mechanism 1106 to deposit build material onto the metalpowder bed 1114.

With reference to FIG. 6A, one or more processors of the controller 1120can execute instructions to control movement of one or more of the metalpowder supply 1112 and the metal powder bed 1114 relative to one anotheras the three-dimensional composition 1102 is being formed. For example,one or more processors of the controller 1120 can execute instructionsto move the metal powder supply 1112 in a z-axis direction toward thespreader 1116 to direct the metal powder 1104 toward the spreader 1116as each layer of the three-dimensional composition 102 is formed and tomove the metal powder bed 1114 in a z-axis direction away from thespreader 1116 to accept each new layer of the metal powder along the topof the metal powder bed 1114 as the spreader 1116 moves across the metalpowder bed 1114. One or more processors of the controller 1120 also maycontrol movement of the spreader 1116 from the metal powder supply 1112to the metal powder bed 1114 to move successive layers of the metalpowder across the metal powder bed 1114.

In some embodiments, one or more processors of the controller 1120 cancontrol movement of the print head 1108 (in FIG. 6B) and/or 1118 (inFIG. 6A) to deposit liquid such as a binder composition onto selectedregions of the metal powder bed 1114 to deliver a respectivepredetermined two-dimensional pattern of the liquid to each new layer ofthe metal powder 1104 along the top of the metal powder bed 1114. Ingeneral, as a plurality of sequential layers of the metal powder 1104are introduced to the metal powder bed 1114 and the predeterminedtwo-dimensional patterns of the liquid are delivered to each respectivelayer of the plurality of sequential layers of the metal powder 1104,the three-dimensional composition 1102 is formed according to thethree-dimensional model (e.g., a model stored in a non-transitory,computer readable storage medium coupled to, or otherwise accessible by,the controller 1120, such as three-dimensional model 1124 stored in thenon-transitory, computer readable storage medium 1122). In certainembodiments, the controller 1120 may retrieve the three-dimensionalmodel (e.g., three-dimensional model 1124) in response to user input,and generate machine-ready instructions for execution by the additivemanufacturing system 1100 to fabricate the three-dimensional object1102.

As described above, it will be appreciated that the illustrativeadditive manufacturing system 1100 is provided as one example of asuitable additive manufacturing system and is not intended to belimiting with respect to the techniques described herein for controllingthe flow behavior of a metal powder. For instance, it will beappreciated that the techniques may be applied within an additivemanufacturing apparatus that utilizes only a roller as a materialdeposition mechanism and does not include material deposition mechanism1106.

According to some embodiments, the techniques described herein forcontrolling the flow behavior of a metal powder may be employed tocontrol properties of a metal powder for a binder jet additivemanufacturing system. Such a system may comprise additive manufacturingsystem 1100 in addition to one or more other apparatus for producing acompleted part (e.g., a metal object as described herein). Suchapparatus may include, for example, a furnace for sintering athree-dimensional composition fabricated by the additive manufacturingsystem 1100 (or for sintering such a three-dimensional compositionsubsequent to applying other post-processing steps upon thethree-dimensional composition).

Techniques described herein may refer to a “metal powder,” although itwill be appreciated that the techniques described herein are notnecessarily limited to use cases in which the metal material employed toform one or more of the articles described herein comprises or consistsof a powder. As such, while the discussion above may focus primarily ondepositing a binder composition onto a metal powder, it will beappreciated that any binder deposition process described herein may alsoapply to deposition of a binder onto any granular material(s).

Referring now to FIG. 7, an additive manufacturing plant 1300 caninclude the additive manufacturing system 1100, a conveyor 1304, and apost-processing station 1306. The metal powder bed 1114 containing thethree-dimensional composition 1102 can be moved along the conveyor 1304and into the post-processing station 1306. The conveyor 1304 can be, forexample, a belt conveyor movable in a direction from the additivemanufacturing system 1100 toward the post-processing station.Additionally, or alternatively, the conveyor 1304 can include a cart onwhich the powder bed 1114 is mounted and, in certain instances, thepowder bed 1114 can be moved from the additive manufacturing system 1100to the post-processing station 1306 through movement of the cart (e.g.,through the use of actuators to move the cart along rails or by anoperator pushing the cart).

In the post-processing station 1306 shown in FIG. 7, thethree-dimensional composition 1102 can be heated in the metal powder bed1114 to remove at least some of the liquid of the binder composition inthe three-dimensional composition and to form a metal-based compositestructure (e.g., a self-supporting metal-based composite structure)within the metal powder bed. The metal-based composite structure can beremoved from the metal powder bed 1114. According to some aspects, thebinder compositions described herein may aid in attaining a desiredmechanical strength characteristic of the metal-based compositestructure, thereby allowing for improved ability to handle themetal-based composite structure and improved consistency in metalobjects formed from such metal-based composite structures. The metalpowder 1104 remaining in the metal powder bed 1114 upon removal of themetal-based composite structure can be, for example, recycled for use insubsequent fabrication of additional parts. Additionally, oralternatively, in the post-processing station 1306, the metal-basedcomposite structure can be cleaned (e.g., through the use of pressurizedair) of excess amounts of the metal powder 1104.

In systems employing a binder jetting process, a metal-based compositestructure can undergo one or more de-binding processes in thepost-processing station 1306 to remove all or a portion of a polymer ofthe binder composition from the metal-based composite structure 1102.Non-limiting examples of suitable de-binding processes can include athermal de-binding process (e.g., heating as described elsewhereherein), a supercritical fluid de-binding process, a catalyticde-binding process, a liquid de-binding process, and combinationsthereof. For example, a plurality of de-binding processes can be stagedto remove components of a binder composition in corresponding stages asthe metal-based composite structure 102 is formed into a metal object.

The post-processing station 1306 shown in FIG. 7 can include a furnace1308. The metal-based composite structure can undergo de-binding in thefurnace 1308. It is also possible for de-binding may take place in alocation other than a furnace or for the de-binding step to be omitted(e.g., for a metal-based composite structure to undergo sinteringwithout undergoing de-binding first). In some embodiments, themetal-based composite structure and/or the de-bound metal structure canundergo sintering in the furnace 1308 such that the metal particles ofthe powder 1106 melt (e.g., to an extent not overall undesirable) andcombine with one another to form a metal object.

As described above, in some embodiments, a binder composition (and/orone or more components thereof) is configured to form one or more of thearticles described herein (e.g., a three-dimensional composition, ametal-based composition) in combination with a metal powder describedherein. In some embodiments, one or more of the articles describedherein may be formed from a binder composition described herein (e.g., ade-bound metal composition, a metal object). Such articles may comprisethe binder composition, may comprise some components of the bindercomposition but lack other components of the binder composition (e.g.,may comprise a polymer present in the binder composition but lack asolvent present in the binder composition), or may not include anycomponents of the binder composition. In some embodiments, an articledescribed herein comprises a reaction product of a binder composition(e.g., a polymer present in the binder composition that has beencross-linked, such as by a cross-linking agent present in the bindercomposition; a thermal decomposition product of a component of thebinder composition, such as char).

As also described above, some binder compositions described herein mayhave one or more physical properties that enhances their suitability foruse in one or more of the methods described herein, such as one or moreof the methods for additive manufacturing described herein, and/or inone or more of the articles described herein, such as athree-dimensional object, a metal-based composite structure, a de-boundmetal structure, and/or a metal object. Further details regarding somesuch physical properties is provided below.

In some embodiments, a binder composition described herein may have anadvantageous viscosity. Without wishing to be bound by any particulartheory, it is believed that the viscosity of the binder composition mayaffect its ability to be printed by a particular print head. Forinstance, some print heads may be designed to print binder compositionshaving a certain range of viscosities and may be unable to printcompositions having viscosities outside of this range in a manner thatis reliable and/or desirable. By way of example, binder compositionshaving viscosities above the range for which the print head isconfigured may not flow or may not flow appreciably at the pressuresprovided by the print head. As another example, binder compositionshaving viscosities below the range for which the print head isconfigured may flow in undesirable manners at the pressures provided bythe print head (e.g., flow in a manner that produces droplets that arecoalesced, take the form a mist, and/or misdirected), resulting in poorcontrol over the deposition of the binder composition from the printhead.

In some embodiments, a binder composition has a viscosity at a printingtemperature of greater than or equal to 0.55 cP, greater than or equalto 1 cP, greater than or equal to 1.5 cP, greater than or equal to 2 cP,greater than or equal to 2.5 cP, greater than or equal to 3 cP, greaterthan or equal to 3.5 cP, greater than or equal to 4 cP, greater than orequal to 5 cP, greater than or equal to 6 cP, greater than or equal to 7cP, greater than or equal to 8 cP, greater than or equal to 10 cP,greater than or equal to 12.5 cP, greater than or equal to 15 cP,greater than or equal to 17.5 cP, greater than or equal to 20 cP,greater than or equal to 22.5 cP, greater than or equal to 25 cP, orgreater than or equal to 27.5 cP. In some embodiments, a bindercomposition has a viscosity at a printing temperature of less than orequal to 30 cP, less than or equal to 27.5 cP, less than or equal to 25cP, less than or equal to 22.5 cP, less than or equal to 20 cP, lessthan or equal to 17.5 cP, less than or equal to 15 cP, less than orequal to 12.5 cP, less than or equal to 10 cP, less than or equal to 8cP, less than or equal to 7 cP, less than or equal to 6 cP, less than orequal to 5 cP, less than or equal to 4 cP, less than or equal to 3.5 cP,less than or equal to 3 cP, less than or equal to 2.5 cP, less than orequal to 2 cP, less than or equal to 1.5 cP, or less than or equal to 1cP. Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.55 cP and less than or equal to 30 cP,greater than or equal to 1 cP and less than or equal to 10 cP, greaterthan or equal to 3 cP and less than or equal to 30 cP, or greater thanor equal to 3 cP and less than or equal to 10 cP). Other ranges are alsopossible. The viscosity of the binder composition may be determined byuse of a cone and plate rheometer operated at a shear rate of 300 s⁻¹.The viscosities described above may be desirable for use with particularprint heads of interest (e.g., piezoelectric print heads, thermal printheads, print heads suitable for ink jet printing). By way of example, insome embodiments, it may be desirable for a binder compositionconfigured to be deposited thermally (e.g., by a thermal print head) tohave a viscosity of greater than or equal to 1 cP and less than or equalto 10 cP at the printing temperature. As another example, in someembodiments, it may be desirable for a binder composition configured tobe deposited piezoelectrically (e.g., by a piezoelectric print head) tohave a viscosity of greater than or equal to 3 cP and less than or equalto 30 cP at the printing temperature.

The printing temperature may be a temperature at which the bindercomposition is ejected from a print head (e.g., by an additivemanufacturing process, by a binder jetting process). In someembodiments, the printing temperature is greater than or equal to 20°C., greater than or equal to 25° C., greater than or equal to 30° C.,greater than or equal to 35° C., or greater than or equal to 40° C. Insome embodiments, the printing temperature is less than or equal to 45°C., less than or equal to 40° C., less than or equal to 35° C., lessthan or equal to 30° C., or less than or equal to 20° C. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 20° C. and less than or equal to 40° C.). Other ranges are alsopossible.

As described above, some binder compositions have pHs that arenon-corrosive to one or more articles with which the binder compositionis configured to contact during formation of a metal-based compositestructure. As also described above, these components may includeportions of a printer, such as a print head, and/or components to beincorporated into a metal-based composite structure, such as a metalpowder. In some embodiments, a binder composition that is a weak acid orthat is a base may be less corrosive to such components than a bindercomposition that is a strong acid. Some binder compositions that areweak acids and/or bases may be non-corrosive to such components. Forbinder compositions configured to be employed with a metal powderparticularly susceptible to corrosion, such as a steel powder, suitablevalues of pH for the binder composition may be higher than for thoseconfigured to be employed with a plurality of particles less susceptibleto corrosion.

In some embodiments, a binder composition has a pH of greater than orequal to 4, greater than or equal to 4.5, greater than or equal to 5,greater than or equal to 5.5, greater than or equal to 6, greater thanor equal to 6.5, greater than or equal to 7, greater than or equal to7.5, greater than or equal to 8, greater than or equal to 8.5, greaterthan or equal to 9 greater than or equal to 9.5, greater than or equalto 10, or greater than or equal to 10.5. In some embodiments, a bindercomposition has a pH of less than or equal to 11, less than or equal to10.5, less than or equal to 10, less than or equal to 9.5, less than orequal to 9, less than or equal to 8.5, less than or equal to 8, lessthan or equal to 7.5, less than or equal to 7, less than or equal to6.5, less than or equal to 6, less than or equal to 5.5, or less than orequal to 5. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 4 and less than or equal to 11,greater than or equal to 5 and less than or equal to 8, greater than orequal to 7 and less than or equal to 11, or greater than or equal to 7and less than or equal to 9). Other ranges are also possible. The pH ofa binder composition may be measured with a pH meter.

In some embodiments, the pH of the binder composition may be selected tobe compatible with the particular type of metal powder it will be usedin combination with. For instance, it may be desirable for bindercompositions suitable for use with ferrous alloys having low chromiumcontents (e.g., below 2 wt %, such as 4140 low alloy steel) to have aweakly basic pH (e.g., greater than or equal to 7 and less than or equalto 11, or greater than or equal to 7 and less than or equal to 9). Asanother example, it may be desirable for binder compositions suitablefor use with steels having appreciable chromium contents (e.g., inexcess of 2 wt %, such as stainless steels and some non-stainlesssteels) to have weakly acidic or weakly basic values of pH (e.g.,greater than or equal to 4 and less than or equal to 11, or greater thanor equal to 5 and less than or equal to 8).

The binder compositions described herein may have a variety of suitablesurface tensions. For instance, in some embodiments, a bindercomposition has a surface tension of greater than or equal to 18dynes/cm, greater than or equal to 20 dynes/cm, greater than or equal to22.5 dynes/cm, greater than or equal to 25 dynes/cm, greater than orequal to 28 dynes/cm, greater than or equal to 30 dynes/cm, greater thanor equal to 32.5 dynes/cm, greater than or equal to 35 dynes/cm, greaterthan or equal to 40 dynes/cm, greater than or equal to 45 dynes/cm,greater than or equal to 50 dynes/cm, greater than or equal to 55dynes/cm, greater than or equal to 60 dynes/cm, or greater than or equalto 65 dynes/cm. In some embodiments, a binder composition has a surfacetension of less than or equal to 70 dynes/cm, less than or equal to 65dynes/cm, less than or equal to 60 dynes/cm, less than or equal to 55dynes/cm, less than or equal to 50 dynes/cm, less than or equal to 45dynes/cm, less than or equal to 40 dynes/cm, less than or equal to 35dynes/cm, less than or equal to 32.5 dynes/cm, less than or equal to 30dynes/cm, less than or equal to 28 dynes/cm, less than or equal to 25dynes/cm, less than or equal to 22.5 dynes/cm, or less than or equal to20 dynes/cm. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 18 dynes/cm and less than orequal to 70 dynes/cm). Other ranges are also possible. The surfacetension of a binder composition may be measured in accordance with ASTMD1331-14.

As described above, in some embodiments, a binder composition as a wholemay comprise a combination of advantageous components. Further detailsregarding such components are provided below.

In some embodiments, a binder composition comprises one or morepolymers. One example of a suitable type of polymer that may be includedin a binder composition is a polymer including an acrylic acid repeatunit, the chemical structure of which is shown below:

Advantageously, the acrylic acid repeat unit may be esterified as partof a cross-linking reaction. The acrylic acid repeat unit may be anacidic repeat unit (e.g., comprising an acidic hydrogen) or may be adeprotonated repeat unit (e.g., it may be deprotonated and negativelycharged, it may be associated with a counter ion). Without wishing to bebound by any particular theory, in some embodiments, a polymer includingat least some acrylic acid repeat units that are deprotonated (e.g.,exclusively acrylic acid repeat units that have been deprotonated, bothacrylic acid repeat units that have been deprotonated and those that areacidic) may be beneficially hygroscopic and/or soluble. This is believedto reduce the latency of the binder formulation and enhance its decapperformance.

Polymers including acrylic acid repeat units may further comprise other,different repeat units. By way of example, a binder composition maycomprise a polymer comprising an acrylic acid repeat unit and comprisingfurther, non-acrylic acid, repeat units (e.g., styrene monomers, maleicanhydride repeat units). The repeat units in a polymer (e.g., acrylicacid repeat units, others) may be distributed within the polymer in avariety of suitable manners (e.g., randomly, statistically,alternatingly, in one or more blocks, etc.). In some embodiments, apolymer may comprise acrylic acid repeat units and may comprise one ormore end groups lacking an acrylic acid functional group (e.g., one ormore initiators, one or more RAFT agents). It is also possible for thepolymer to be a homopolymer comprising acrylic acid repeat units. By wayof example, a binder composition may comprise poly(acrylic acid).

When a polymer comprising an acrylic acid repeat unit further comprisesother repeat units, the acrylic acid repeat unit may make up a varietyof suitable amounts of the polymer. In some embodiments, a polymercomprises an acrylic acid repeat unit that makes up greater than orequal to 30 mol %, greater than or equal to 40 mol %, greater than orequal to 50 mol %, greater than or equal to 60 mol %, greater than orequal to 70 mol %, greater than or equal to 80 mol %, or greater than orequal to 90 mol % of the repeat units within the polymer. In someembodiments, a polymer comprises an acrylic acid repeat unit make upless than or equal to 100 mol %, less than or equal to 90 mol %, lessthan or equal to 80 mol %, less than or equal to 70 mol %, less than orequal to 60 mol %, less than or equal to 50 mol %, or less than or equalto 40 mol % of the repeat units within the polymer. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 30 mol % and less than or equal to 100 mol %). Other ranges are alsopossible.

Further examples of suitable polymers for use in binder compositionsinclude synthetic polymers and natural polymers. Non-limiting examplesof suitable synthetic polymers include poly(ethylenimine)s (which may bea suitable cross-linking agent as described elsewhere herein),poly(vinyl alcohol), and poly(vinyl pyrrolidone). Non-limiting examplesof suitable natural polymers include chitosan, gelatin, starches, andsugars.

In some embodiments, a binder composition comprises a low molecularweight polymer (e.g., a low molecular weight polymer including anacrylic acid repeat unit). Advantageously low molecular weight polymersmay increase the viscosity of binder compositions to a smaller extentthan otherwise equivalent polymers having a higher molecular weight.This may desirably allow for binder compositions to be formulated thatboth have a beneficial viscosity and include a larger wt % of polymer.Increased amounts of polymer in the binder composition are believed toenhance the transverse flexural strength of articles formed therefrom(e.g., metal-based composite structures). Lower molecular weightpolymers are also believed to be beneficial because it is believed thatthey are more soluble in many binder formulations than otherwiseequivalent polymers having a higher molecular weight. This enhancedsolubility is believed to result in improved binder jetting performance(e.g., improved latency and/or decap performance).

A binder composition described herein may comprise a polymer (e.g., apolymer including an acrylic acid repeat unit) having a weight averagemolecular weight of less than or equal to 40 kDa, less than or equal to35 kDa, less than or equal to 30 kDa, less than or equal to 25 kDa, lessthan or equal to 20 kDa, less than or equal to 15 kDa, less than orequal to 10 kDa, less than or equal to 7.5 kDa, less than or equal to 6kDa, less than or equal to 5 kDa, less than or equal to 4 kDa, less thanor equal to 3 kDa, less than or equal to 2 kDa, or less than or equal to1 kDa. In some embodiments, the binder composition comprises a polymer(e.g., a polymer including an acrylic acid repeat unit) having a weightaverage molecular weight of greater than or equal to 500 Da, greaterthan or equal to 1 kDa, greater than or equal to 2 kDa, greater than orequal to 3 kDa, greater than or equal to 4 kDa, greater than or equal to5 kDa, greater than or equal to 6 kDa, greater than or equal to 7.5 kDa,greater than or equal to 10 kDa, greater than or equal to 15 kDa,greater than or equal to 20 kDa, greater than or equal to 30 kDa, orgreater than or equal to 35 kDa. In some embodiments, a bindercomposition comprises a polymer having a weight average molecular weightof Combinations of the above-referenced ranges are also possible (e.g.,less than or equal to 40 kDa and greater than or equal to 500 Da, lessthan or equal to 40 kDa and greater than or equal to 2 kDa, or less thanor equal to 6 kDa and greater than or equal to 2 kDa). Other ranges arealso possible. The weight average molecular weight may be determined byGPC.

It should also be understood that a single type of polymer present in abinder composition (e.g., a polymer including an acrylic acid repeatunit, a polymer lacking an acrylic acid repeat unit) may have a weightaverage molecular weight in one or more of the above-referenced ranges(e.g., in a binder composition that further comprises other, differenttypes of polymers or that lacks other, different polymers) and/or thebinder composition may comprise more than one type of polymer and all ofthe types of polymers together may have a weight average molecularweight in one or more of the above-referenced ranges.

In some embodiments, a binder composition comprises both a low molecularweight polymer (e.g., a polymer comprising an acrylic acid repeat unit)and further comprises a non-low molecular weight polymer. The non-lowmolecular weight polymer may have a molecular weight outside of one ormore of the ranges described above (e.g., of greater than 40 kDa). Insome embodiments, the non-low molecular weight polymer comprises apolymer lacking an acrylic acid repeat unit (e.g., a binder compositionmay comprise synthetic polymer and/or a natural polymer as describedabove that is also a non-low molecular weight polymer).

Polymers suitable for use in the binder compositions described hereinmay be present in the binder compositions in a variety of suitableamounts. In some embodiments, a binder composition comprises a polymeror combination of polymers that make up greater than or equal to 1 wt %,greater than or equal to 2 wt %, greater than or equal to 3 wt %,greater than or equal to 4 wt %, greater than or equal to 5 wt %,greater than or equal to 7.5 wt %, greater than or equal to 10 wt %,greater than or equal to 15 wt %, greater than or equal to 20 wt %,greater than or equal to 25 wt %, greater than or equal to 30 wt %, orgreater than or equal to 35 wt % of the binder composition. In someembodiments, a binder composition comprises a polymer or combination ofpolymers that make up less than or equal to 40 wt %, less than or equalto 35 wt %, less than or equal to 30 wt %, less than or equal to 25 wt%, less than or equal to 20 wt %, less than or equal to 15 wt %, lessthan or equal to 10 wt %, less than or equal to 7.5 wt %, less than orequal to 5 wt %, less than or equal to 4 wt %, less than or equal to 3wt %, or less than or equal to 1 wt % of the binder composition.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 1 wt % and less than or equal to 40 wt %,greater than or equal to 1 wt % and less than or equal to 30 wt %,greater than or equal to 1 wt % and less than or equal to 25 wt %,greater than or equal to 2 wt % and less than or equal to 30 wt %, orgreater than or equal to 3 wt % and less than or equal to 40 wt %).Other ranges are also possible. It should also be understood that asingle polymer may be present in a binder composition in one or more ofthe above-referenced ranges (e.g., that further comprises other,different polymers or that lacks other, different polymers) and/or thetotal amount of polymer in a binder composition may be in one or more ofthe above-referenced ranges.

In some embodiments, a binder composition comprises one or morecross-linking agents. The cross-linking agent(s) may be configured tocross-link one or more polymers also present in the binder composition.This may advantageously cause the polymer(s) to form a cross-linkednetwork with enhanced cohesive strength, which may enhance themechanical properties (e.g., flexural strength) of a metal-basedcomposite structure formed from the binder composition.

When present, a cross-linking agent may be configured to cross-link oneor more polymers in a variety of suitable manners. For instance, in someembodiments, a cross-linking agent is configured to undergo a reactionwith one or more functional groups on a polymer. By way of example, across-linking agent may comprise a nucleophilic functional group that isconfigured to undergo a reaction with an electrophilic functional groupincluded in the polymer (e.g., an acrylic acid repeat unit).Non-limiting examples of suitable nucleophilic functional groups includealcohol-based functional groups (e.g., hydroxyl functional groups),amino functional groups, thiol functional groups, and epoxide functionalgroups. Non-limiting examples of suitable cross-linking agentscomprising such functional groups include poly(ethylenimine)s, polyols(e.g., aliphatic diols such as 1,2-hexanediol, 1,3-hexanediol,1,2-butanediol, 1,4-cyclohexane diol, ethylene diol, diethylene glycol,and/or propylene glycol; aliphatic triols such as glycerol; aliphatictetrols, such as erythritol), aliphatic poly(ether)s (e.g.,poly(propylene glycol), poly(ethylene glycol)), multifunctional amines(e.g., diethanolamine, triethanolamine), multifunctional thiols, andmetallic cross-linking agents (e.g., zirconium carbonate, titaniumisopropoxides, aluminum isopropoxides).

The cross-linking agents described herein typically comprise at leasttwo portions configured to undergo a reaction with a polymer (e.g., atleast two nucleophilic functional groups). In other words, thecross-linking agents described herein are typically at leastdifunctional. In some embodiments, a binder composition comprises across-linking agent that is difunctional, trifunctional,tetrafunctional, or having a higher level of functionality.

Cross-linking agents suitable for use in the binder compositionsdescribed herein may have a variety of suitable molecular weights. Insome embodiments, a binder composition comprises a cross-linking agenthaving a weight average molecular weight of less than or equal to 2 kDa,less than or equal to 1 kDa, less than or equal to 750 Da, less than orequal to 500 Da, less than or equal to 200 Da, less than or equal to 100Da, or less than or equal to 75 Da. In some embodiments, a bindercomposition comprises a cross-linking agent having a weight averagemolecular weight of greater than or equal to 62 Da, greater than orequal to 75 Da, greater than or equal to 100 Da, greater than or equalto 200 Da, greater than or equal to 500 Da, greater than or equal to 750Da, or greater than or equal to 1 kDa. Combinations of theabove-referenced ranges are also possible (e.g., less than or equal to 2kDa and greater than or equal to 62 Da). Other ranges are also possible.The weight average molecular weight may be determined by GPC.

It should also be understood that a single type of cross-linking agentpresent in a binder composition may have a weight average molecularweight in one or more of the above-referenced ranges (e.g., in a bindercomposition that further comprises other, different types ofcross-linking agents or that lacks other, different cross-linkingagents) and/or the binder composition may comprise more than one type ofcross-linking agents and all of the types of cross-linking agentstogether may have a weight average molecular weight in one or more ofthe above-referenced ranges.

Cross-linking agents suitable for use in the binder compositionsdescribed herein may be present in the binder compositions in a varietyof suitable amounts. In some embodiments, a binder composition comprisesa cross-linking agent or combination of cross-linking agents that makeup greater than or equal to 0 wt %, greater than or equal to 0.1 wt %,greater than or equal to 0.2 wt %, greater than or equal to 0.3 wt %,greater than or equal to 0.4 wt %, greater than or equal to 0.5 wt %,greater than or equal to 0.75 wt %, greater than or equal to 1 wt %,greater than or equal to 1.5 wt %, greater than or equal to 2 wt %,greater than or equal to 5 wt %, or greater than or equal to 7.5 wt % ofthe binder composition. In some embodiments, a binder compositioncomprises cross-linking agent or combination of cross-linking agentsthat make up less than or equal to 10 wt %, less than or equal to 7.5 wt%, less than or equal to 5 wt %, less than or equal to 2 wt %, less thanor equal to 1.5 wt %, less than or equal to 1 wt %, less than or equalto 0.75 wt %, less than or equal to 0.5 wt %, less than or equal to 0.4wt %, less than or equal to 0.3 wt %, less than or equal to 0.2 wt %, orless than or equal to 0.1 wt % of the binder composition. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to 0 wt % and less than or equal to 10 wt %, greater than or equalto 0.1 wt % and less than or equal to 10 wt %, or greater than or equalto 0.2 wt % and less than or equal to 10 wt %). Other ranges are alsopossible. It should also be understood that a single cross-linking agentmay be present in a binder composition in one or more of theabove-referenced ranges (e.g., that further comprises other, differentcross-linking agents or that lacks other, different cross-linkingagents) and/or the total amount of cross-linking agent in a bindercomposition may be in one or more of the above-referenced ranges.

In some embodiments, a binder composition comprises a solvent. Thesolvent may solvate the other components therein (e.g., one or morepolymers therein, one or more pH modifiers therein, one or moresurfactants therein, one or more biocides therein, one or morehumectants therein, one or more adhesion promoters therein, one or morecross-linking agents therein). In some embodiments, the solvent is aliquid and/or the binder composition is a liquid solution.

In some embodiments, a binder composition comprises a solvent comprisingwater. In other words, a binder composition may comprise an aqueoussolvent and/or an aqueous solution. Without wishing to be bound by anyparticular theory, it is believed that aqueous solvents may be desirablefor use in binder compositions because they may be more environmentallyfriendly and/or less toxic than other types of solvents (e.g., thanorganic solvents). It is also believed that, when water is a reactionproduct of a cross-linking reaction that one or more components of thebinder composition are configured to undergo, the presence of water inthe binder composition may advantageously suppress cross-linking atpoints in time before it is desired. Then, the water may be removed andcross-linking may be performed.

Solvents suitable for use in the binder compositions described hereinmay be present in the binder compositions in a variety of suitableamounts. In some embodiments, a binder composition comprises a solventthat makes up greater than or equal to 50 wt %, greater than or equal to55 wt %, greater than or equal to 60 wt %, greater than or equal to 65wt %, greater than or equal to 70 wt %, greater than or equal to 75 wt%, greater than or equal to 80 wt %, greater than or equal to 85 wt %,greater than or equal to 90 wt %, or greater than or equal to 95 wt % ofthe binder composition. In some embodiments, a binder compositioncomprises a solvent that makes up less than or equal to 99 wt %, lessthan or equal to 95 wt %, less than or equal to 90 wt %, less than orequal to 85 wt %, less than or equal to 80 wt %, less than or equal to75 wt %, less than or equal to 70 wt %, less than or equal to 65 wt %,less than or equal to 60 wt %, or less than or equal to 55 wt % of thebinder composition. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 50 wt % and less than or equalto 99 wt %). Other ranges are also possible.

Binder compositions comprising a solvent may also comprise one or moreco-solvents. The co-solvent(s) may enhance the solubility of one or morecomponents of the binder composition in the solvent (e.g., it mayenhance the solubility of one or more polymers, one or more pHmodifiers, one or more surfactants, one or more biocides, one or morehumectants, one or more adhesion promoters, and/or one or morecross-linking agents in the binder composition). The co-solvent(s) maybe liquid(s).

Non-limiting examples of suitable co-solvents include solvents that aremiscible with the solvent and readily solubilize one or more componentsof the binder composition. For instance, when the solvent compriseswater and the binder composition comprises one or more organiccomponents, one or more water-soluble organic solvents may be suitablefor use as co-solvents. Non-limiting examples of suitable co-solventsinclude alcohols (e.g., monofunctional alcohols, diols, triols), ketones(e.g., acetone, diacetone, butanone), esters (e.g., ethyl acetate),ethers, lactones (e.g., hydroxybutyrolactone), lactams, pyrrolidones(e.g., N-methyl pyrrolidone, N-phenyl pyrrolidone, 2-pyrrolidone),amides (e.g., dimethyl acetamide), sulfones (e.g., dimethyl sulfone),and sulfoxides (e.g., dimethyl sulfoxide). Further examples of alcoholsinclude methanol, ethanol, isopropanol, 1-butanol, 2-butanol,1,2-hexanediol, ethylene glycol, propylene glycol,1-(1-hydroxypropoxy)propan-1-ol, 1-(2-hydroxypropoxy)propan-2-ol,3,3′-oxybis(propan-1-ol), and dipropylene glycol (a mixture of isomers1-(1-hydroxypropoxy)propan-1-ol, 1-(2-hydroxypropoxy)propan-2-ol, and3,3′-oxybis(propan-1-ol)).

Co-solvents suitable for use in the binder compositions described hereinmay be present in the binder compositions in a variety of suitableamounts. In some embodiments, a binder composition comprises aco-solvent or combination of co-solvents that make up greater than orequal to 0 wt %, greater than or equal to 1 wt %, greater than or equalto 2 wt %, greater than or equal to 3 wt %, greater than or equal to 4wt %, greater than or equal to 5 wt %, greater than or equal to 7.5 wt%, greater than or equal to 10 wt %, greater than or equal to 15 wt %,greater than or equal to 20 wt %, or greater than or equal to 25 wt % ofthe binder composition. In some embodiments, a binder compositioncomprises a co-solvent or combination of co-solvents that make up lessthan or equal to 30 wt %, less than or equal to 25 wt %, less than orequal to 20 wt %, less than or equal to 15 wt %, less than or equal to10 wt %, less than or equal to 7.5 wt %, less than or equal to 5 wt %,less than or equal to 4 wt %, less than or equal to 3 wt %, less than orequal to 2 wt %, or less than or equal to 1 wt % of the bindercomposition. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0 wt % and less than or equalto 30 wt %, or greater than or equal to 0 wt % and less than or equal to5 wt %). Other ranges are also possible. It should also be understoodthat a single co-solvent may be present in a binder composition in oneor more of the above-referenced ranges (e.g., that further comprisesother, different co-solvents or that lacks other, different co-solvents)and/or the total amount of co-solvent in a binder composition may be inone or more of the above-referenced ranges.

In some embodiments, a binder composition comprises an adhesionpromoter. An adhesion promoter is a component of a binder compositionthat facilitates adhesion between one or more components of the bindercomposition and a metal powder. For example, an adhesion promoter mayfacilitate adhesion between a low molecular weight polymer (e.g., apolymer comprising an acrylic acid repeating unit) and a metal powderduring at least a portion of an additive manufacturing process. It hasbeen observed in the context of this disclosure that in someembodiments, improved adhesion afforded by inclusion of adhesionpromoters in a binder composition can improve binder performance withmetal powders relative to binder compositions lacking such an adhesionpromoter. It should be understood that in this context, adhesion betweenone or more components of a binder composition and a metal powder refersto any of a variety of specific and non-specific physical and/orchemical interactions that hold the component and the metal powdertogether. For example, an adhesion promoter may facilitate adhesionbetween a component of the binder composition (e.g., a low molecularweight polymer comprising an acrylic acid repeating unit) by forming oneor more chemical bonds (e.g., covalent, hydrogen, and/or ionic bonds)with the component and/or with the metal powder. As other examples, theadhesion promoter may facilitate adhesion between a component of thebinder composition by electrostatic, dispersive, and/or hydrogen-bondinginteractions between the component the metal powder. In some instances,adhesion promoters described herein may be particularly useful withcertain types of metal powders such as precious metal powders (e.g.,comprising gold metal and/or a gold alloy, silver metal and/or a silveralloy, or platinum metal and/or a platinum alloy).

In some embodiments, the adhesion promoter in the binder composition isa molecule. For example, the adhesion promoter may be a small molecule(e.g., having a molecular weight of less than 1000 Da, less than orequal to 750 Da, less than or equal to 500 Da, less than or equal to 300Da, and/or as low as 200 Da, as low as 100 Da, or lower). In someembodiments, the adhesion promoter is a polymer (e.g., repeating unitsand a weight average molecular weight of greater than or equal to 1 kDa,greater than or equal to 1.5 kDa, greater than or equal to 2 kDa,greater than or equal to 5 kDa, and/or up to 10 kDa, up to 20 kDa, up to40 kDa, or greater).

In some embodiments, the adhesion promoter comprises a functional groupcapable of binding to the metal powder. A choice of functional group forthe adhesion promoter may depend on the composition of the metal powder.For example, the functional group of the adhesion promoter may beselected based on known reactivity with the metal/metal alloy and/or aknown binding affinity with the metal/metal alloy. Examples of possiblefunctional groups include, but are not limited to thiols, disulfides,carboxylic acids/carboxylates, amines, and hydroxy groups. A functionalgroup capable of binding to a metal powder may be capable of forming achemical bond with the metal powder. The chemical bond (e.g., a covalentbond, an ionic bond) may be relatively strong. For example, thefunctional group may be capable of forming a chemical bond having a bonddissociation energy of greater than or equal to 50 kJ/mol, greater thanor equal to 75 kJ/mol, greater than or equal to 100 kJ/mol, greater thanor equal to 120 kJ/mol, and/or up to 130 kJ/mol, up to 150 kJ/mol, up to200 kJ/mol, or higher at 298 K. It should be understood that in thecontext of this disclosure, binding (e.g., via formation of a chemicalbond) between a functional group and a metal powder encompasses formingnon-covalent affinity-based interactions as well as undergoingbond-forming reactions such as dative/coordination bonding, reactionsinvolving acid-base interactions (including those involvingprotonation/deprotonation), reactions involvingnucleophilic/electrophilic substitutions, reactions involvingradical-based coupling/decoupling, and/or reactions involving reductionor oxidation.

In some embodiments, the functional group capable of binding to themetal powder is a sulfur-containing functional group. Examples ofsulfur-containing functional groups the adhesion promoter may compriseinclude, but are not limited to, thiols, disulfides, thioethers,thioesters, sulfonyl groups, sulfoxide groups, sulfinic acid groups,sulfonate ester groups, thiocyanates, thioketones, thials, andthiocarboxylate/thiocarboxylic acid groups. It has been observed in thecontext of this disclosure that in some embodiments, adhesion promoterscomprising sulfur-containing functional groups may promote beneficialadhesion with certain metal powders, such as precious metal powders. Forexample, it has been observed that metal powders comprising gold metaland/or gold alloys (e.g., rose gold) may bind relatively strongly toadhesion promoters comprising sulfur-containing functional groups (e.g.,thiol-containing functional groups). Without wishing to be bound by anyparticular theory, it is believed that sulfur-containing functionalgroups such as thiols can form relatively strong bonds with gold. FIG.9A depicts an illustrative reaction scheme showing adhesion betweenmetal powder particle 50 (e.g., a gold particle) with sulfur-containingadhesion promoters 60 (e.g., cysteine molecules), according to certainembodiments.

In some embodiments, the functional group capable of binding to themetal powder (e.g., a sulfur-containing functional group) is a firstfunctional group of the adhesion promoter, and the adhesion promotercomprises a second functional group. The second functional group may becapable of promoting adhesion with one or more components of the bindercomposition. For example, the second functional group may be capable ofundergoing a chemical reaction to form a chemical bond with a lowmolecular weight polymer of the binder composition (e.g., comprisingacrylic acid repeat units). Forming a chemical bond between the adhesionpromoter and the low molecular weight polymer may be performed under anyof a variety of suitable conditions known in the art, such as viaheating, applying electromagnetic radiation (e.g., UV or visible light),and/or adding reaction initiators such as suitable catalyst. The secondfunctional group may react with a backbone of the polymer, or a residueof the polymer.

In some embodiments, the second functional group comprises anucleophilic functional group. Examples of potentially suitablenucleophilic functional groups include, but are not limited to, aminegroups and hydroxyl groups. The nucleophilic groups of the adhesionpromoter may react to result in a bond with an electrophilic functionalgroup of a polymer of the binder compositions. As an illustrativeexample, an adhesion promoter may facilitate adhesion between a metalpowder (e.g., comprising gold metal and/or gold alloy) and a polymercomprising acrylic acid repeating units by binding a first functionalgroup (e.g., thiol) to the metal particle and reacting a secondfunctional group (e.g., an amine) with the carboxylic acid groups of theacrylic acid polymer to afford an amide bond. In some embodiments, thefirst functional group is a sulfur-containing functional group and thesecond functional group is a nucleophilic group. Molecular examples ofsuch an adhesion promoter includes amine thiols, dithiothreitol, andmercaptoethanol. A polymeric example of such an adhesion promoter is athiolated polyvinyl alcohol.

In some embodiments, the second functional group comprises anelectrophilic functional group. Examples of potentially suitableelectrophilic functional groups include, but are not limited to,carboxylate/carboxylic acid groups, aldehydes, ketones, and groupscomprising leaving groups such as halides, tosylates, succinimidylgroups, and the like. The electrophilic functional groups of theadhesion promoter may react to result in a bond with nucleophilicfunctional group of a polymer of the binder compositions. As anillustrative example, an adhesion promoter may facilitate adhesionbetween a metal powder (e.g., comprising gold metal and/or gold alloy)and a polymer comprising hydroxy or amine repeating units (e.g.,polyvinyl alcohol or polyethylene imine, respectively) by binding afirst functional group (e.g., thiol) to the metal particle and reactinga second functional group (e.g., a carboxylic acid/carboxylate) with thehydroxy or amine groups of the polymer to afford an ester or amide bond.In some embodiments, the first functional group is a sulfur-containingfunctional group and the second functional group is an electrophilicfunctional group. Examples of such an adhesion promoter include, but arenot limited to, thiocarboxylic acids, and thiocarboxylates. FIG. 9Bshows an illustrative reaction scheme showing a bond-forming reactionbetween adhesion promoters 60 comprising thiol groups bound to metalpowder 50 (e.g., comprising gold metal and/or gold alloy) andcarboxylate electrophilic groups, with polyvinyl alcohol of a bindercomposition, according to certain embodiments.

In some embodiments, the adhesion promoter comprises a first functionalgroup capable of binding to a metal powder, a second functional group,and a third functional group. As in the case of the second functionalgroup, the third functional group may be a nucleophilic functional groupor an electrophilic functional group. In some embodiments, the secondfunctional group is a nucleophilic functional group and the thirdfunctional group is an electrophilic functional group (or equivalently,the second functional group is an electrophilic group and the thirdfunctional group is a nucleophilic group). It is believed that anadhesion promoter comprising both a nucleophilic functional group and anelectrophilic functional group can, in some instances, affordmanufacturing and binder formulation choice flexibility by being able toreact with either nucleophilic group-containing polymers (e.g.,polyvinyl alcohol) or electrophilic functional group-containing polymers(e.g., polymers with acrylic acid repeating units) of the bindercomposition. Examples of such adhesion promoters includesulfur-containing amino acids. For example, the adhesion promoter may beor comprise cysteine (e.g., L-cysteine) or its oxidation product cystine(comprising a disulfide bond). The adhesion promoter may, alternativelybe or comprise methionine, homocysteine, and/or taurine. Referring againto FIGS. 9A-9B, adhesion promoters 60 are cysteine molecules eachcomprising a thiol, a carboxylate, and an amine, in accordance withcertain embodiments.

The adhesion promoter may be present in a binder composition in any of avariety of suitable amounts. In some embodiments, the weight percentageof the adhesion promoter in the binder composition is greater than orequal to 0.1 wt %, greater than or equal to 0.2 wt %, greater than orequal to 0.5 wt %, greater than or equal to 1 wt %, greater than orequal to 1.5 wt %, greater than or equal to 2 wt %, greater than orequal to 3 wt %, greater than or equal to 5 wt %, greater than or equalto 10 wt %, or higher. In some embodiments, the weight percentage of theadhesion promoter in the binder composition is less than or equal to 40wt %, less than or equal to 30 wt %, less than or equal to 20 wt %, lessthan or equal to 15 wt %, less than or equal to 10 wt %, less than orequal to 8 wt %, less than or equal to 5 wt %, less than or equal to 4wt %, less than or equal to 3 wt %, or less. Combinations of theseranges are possible. For example, in some embodiments the weightpercentage of the adhesion promoter in the binder composition is greaterthan or equal to 0.1 wt % and less than or equal to 40 wt %, or greaterthan or equal to 0.1 wt % and less than or equal to 10 wt %.

In some embodiments, a binder composition comprises one or more pHmodifiers. The pH modifier(s) may be configured to interact with theother components of the binder composition to adjust the pH to a desiredvalue. For instance, the pH modifier may be configured to interact withthe other components of the binder composition to adjust the pH to avalue that will not appreciably corrode one or more articles with whichthe binder composition is configured to contact during formation of acomposite structure.

The binder compositions described herein may comprise pH modifier(s)that are basic. A variety of types of bases may be suitable for use aspH modifiers. For instance, examples of suitable pH modifiers includeArrhenius bases, Lewis bases, and Bronsted-Lowry bases. As anotherexample, a binder composition may comprise an inorganic base and/or anorganic base. Non-limiting examples of suitable pH modifiers includehydroxides (e.g., sodium hydroxide, potassium hydroxide, lithiumhydroxide), carbonates (e.g., sodium carbonate, potassium carbonate,lithium carbonate), ammonia, tetramethyl ammonium hydroxide, andamine-containing species (e.g., organic amine-containing species thatmay be aliphatic or aromatic, such as methyl amine, ethyl amine,triethyl amine, ethanolamine, triethanolamine, diaminobenzene), andamine derivatives (e.g., pyridine, imidazole).

The pH modifiers described herein may be selected such that the pH ofthe binder composition is in a desirable range. In some embodiments, apH modifier is selected such that the pH of the binder composition isgreater than or equal to 4, greater than or equal to 4.5, greater thanor equal to 5, greater than or equal to 5.5, greater than or equal to 6,greater than or equal to 6.5, greater than or equal to 7, greater thanor equal to 7.5, greater than or equal to 8, greater than or equal to8.5, greater than or equal to 9 greater than or equal to 9.5, greaterthan or equal to 10, or greater than or equal to 10.5. In someembodiments, a binder composition has a pH of less than or equal to 11,less than or equal to 10.5, less than or equal to 10, less than or equalto 9.5, less than or equal to 9, less than or equal to 8.5, less than orequal to 8, less than or equal to 7.5, less than or equal to 7, lessthan or equal to 6.5, less than or equal to 6, less than or equal to5.5, or less than or equal to 5. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 4 and less thanor equal to 11, greater than or equal to 5 and less than or equal to 8,greater than or equal to 7 and less than or equal to 11, or greater thanor equal to 7 and less than or equal to 9). Other ranges are alsopossible.

The pH modifiers described herein may have a variety of suitable boilingpoints. In some embodiments, it may be advantageous for a pH modifier tohave a relatively low boiling point, as this may facilitate removal ofthe pH modifier from the binder composition (or from a three dimensionalcomposition and/or metal-based composite structure fabricated from abinder composition) at relatively low temperatures. This property may beadvantageous when it is desirable to remove the pH modifier from athree-dimensional composition and/or metal-based composite structureinto which it has been incorporated during one of the steps describedherein (e.g., a drying and/or heating step) and/or prior to performingsome of the steps described herein (e.g., a further heating step). Asone specific example, it may be advantageous to remove the pH modifierfrom binder composition prior to cross-linking, as the pH modifier mayinterfere with the cross-linking reaction in certain cases. Theinclusion of such a pH modifier in the binder composition may desirablysuppress cross-linking at points in time before it is desired. In otherembodiments, a pH modifier may also function as a cross-linking agent.

In some embodiments, a binder composition comprises a pH modifier havinga boiling point of less than or equal to 150° C., less than or equal to125° C., less than or equal to 100° C., less than or equal to 75° C.,less than or equal to 50° C., less than or equal to 25° C., less than orequal to 0° C., or less than or equal to −25° C. In some embodiments, abinder composition comprises a pH modifier having a boiling point ofgreater than or equal to −40° C., greater than or equal to −25° C.,greater than or equal to 0° C., greater than or equal to 25° C., greaterthan or equal to 50° C., greater than or equal to 75° C., greater thanor equal to 100° C., or greater than or equal to 125° C. Combinations ofthe above-referenced ranges are also possible (e.g., less than or equalto 150° C. and greater than or equal to −40° C.). Other ranges are alsopossible.

In some embodiments, a binder composition comprises one or morecorrosion inhibitors. The corrosion inhibitor(s) may reduce the amountof corrosion that a plurality of metal particles undergoes when incontact with the binder composition (e.g., in comparison to thecorrosion that the plurality of metal particles would undergo when incontact with an otherwise equivalent binder composition lacking thecorrosion inhibitor). This may be particularly useful for bindercompositions configured to be employed in combination with metal powdersparticularly prone to corrosion, such as metal powders comprising toolsteel. Some corrosion inhibitors suitable for use in the bindercompositions described herein may also be suitable for use as pHmodifiers. The binder compositions described herein may comprise pHmodifiers that are not corrosion inhibitors, corrosion inhibitors thatare not pH modifiers, and pH modifiers that are corrosion inhibitors.

Non-limiting examples of suitable corrosion inhibitors include amines(e.g., triethanol amine, hexamine, phenylenediamine, monoethanol amine),amine salts (e.g., triethanol amine salts of decacarboxylic acid),hydrazine, benzotriazole, and poly(ethyleneimine). In some embodiments,a binder composition comprises one or more surfactant(s).

The surfactant(s) may increase the penetration of the binder compositioninto a composite layer and/or may enhance the jetting performance of thebinder composition. It is also believed that the surfactants mayincrease the amount of spreading of the binder composition in a powderlayer. In some embodiments, the surfactant(s) may reduce the level offoaming in the binder composition during one or more processesassociated with additive manufacturing (e.g., transport to and/ordeposition by a print head) and/or may enhance the rate at which thebinder composition can refill a print head (e.g., a thermal print head).

Some binder compositions may comprise ionic surfactants and some bindercompositions may comprise non-ionic surfactants. Non-limiting examplesof suitable ionic surfactants include sulfates (e.g., ammonium laurylsulfate, sodium lauryl sulfate, sodium laureth sulfate, sodium myrethsulfate, perfluorooctanesulfonate, perfluorobutanesulfonate),sulfosuccinates (e.g., dioctyl sodium sulfosuccinate), ethers (e.g.,alkyl-aryl ether phosphates, alkyl ether phosphates), sodium stearate,sodium lauroyl sarcosinate, perfluorononanoate, and perfluorooctanoate.Non-limiting examples of suitable non-ionic surfactants include Surfynol440, Surfynol 2502, Surfynol 604, Thetawet TS 8230, and ThetawetFS-8150, polyoxyl 35 castor oil, lauryldimethylamine oxide, TritonX-100, and Dynol 604.

In some embodiments, a binder composition comprises a surfactant orcombination of surfactants that make up greater than or equal to 0 wt %,greater than or equal to 0.01 wt %, greater than or equal to 0.02 wt %,greater than or equal to 0.05 wt %, greater than or equal to 0.075 wt %,greater than or equal to 0.1 wt %, greater than or equal to 0.2 wt %,greater than or equal to 0.3 wt %, greater than or equal to 0.4 wt %,greater than or equal to 0.5 wt %, greater than or equal to 0.6 wt %,greater than or equal to 0.7 wt %, greater than or equal to 0.8 wt %, orgreater than or equal to 0.9 wt % of the binder composition. In someembodiments, a binder composition comprises a surfactant or combinationof surfactants that make up less than or equal to 1 wt %, less than orequal to 0.9 wt %, less than or equal to 0.8 wt %, less than or equal to0.7 wt %, less than or equal to 0.6 wt %, less than or equal to 0.5 wt%, less than or equal to 0.4 wt %, less than or equal to 0.3 wt %, lessthan or equal to 0.2 wt %, less than or equal to 0.1 wt %, less than orequal to 0.075 wt %, less than or equal to 0.05 wt %, less than or equalto 0.02 wt %, or less than or equal to 0.01 wt % of the bindercomposition. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0 wt % and less than or equalto 1 wt %, greater than or equal to 0.01 wt % and less than or equal to1 wt %, greater than or equal to 0.01 wt % and less than or equal to0.05 wt %, greater than or equal to 0.1 wt % and less than or equal to 1wt %, greater than or equal to 0.1 wt % and less than or equal to 0.5 wt%, or greater than or equal to 0.5 wt % and less than or equal to 1 wt%). Other ranges are also possible. It should also be understood that asingle surfactant may be present in a binder composition in one or moreof the above-referenced ranges (e.g., that further comprises other,different surfactants or that lacks other, different surfactants) and/orthe total amount of surfactant in a binder composition may be in one ormore of the above-referenced ranges.

In some embodiments, a binder composition comprises one or morebiocide(s). The biocide(s) may inhibit the growth of biological species(e.g., bacteria, yeast, fungi) in the binder composition during storageand/or inhibit enzymatic degradation of a polymer in the bindercomposition during storage. Without wishing to be bound by anyparticular theory, it is believed that biologically-derived polymers,such as chitosan and gelatin, may be particularly susceptible to suchdegradation.

Binder compositions described herein may comprise one or more biocidesthat are microbicides and/or one or more biocides that are fungicides.In some embodiments, a binder composition comprises a biocide that is anisothiazolinone, such as ProxelGXL, 1,2-benzisothiazolin-3-one,4,5-Dichloro-2-octyl-4-isothiazolin-3-one, and2-n-Octyl-4-Isothiazolin-3-One. Further examples of suitable biocidesinclude 3-(3,4-dichlorophenyl)-1,1-dimethylure,2-bromo-2-nitropropane-1,3-diol, lauryldimethylamine oxide, benzalkoniumchloride, and/or rotenone.

In some embodiments, a binder composition comprises a biocide orcombination of biocides that make up greater than or equal to 0 wt %,greater than or equal to 0.01 wt %, greater than or equal to 0.02 wt %,greater than or equal to 0.05 wt %, greater than or equal to 0.075 wt %,greater than or equal to 0.1 wt %, greater than or equal to 0.15 wt %,or greater than or equal to 0.2 wt % of the binder composition. In someembodiments, a binder composition comprises a biocide or combination ofbiocides that make up less than or equal to 0.25 wt %, less than orequal to 0.2 wt %, less than or equal to 0.15 wt %, less than or equalto 0.1 wt %, less than or equal to 0.075 wt %, less than or equal to0.05 wt %, less than or equal to 0.02 wt %, or less than or equal to0.01 wt % of the binder composition. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0 wt % and less than or equal to 0.25 wt %). Other ranges are alsopossible. It should also be understood that a single biocide may bepresent in a binder composition in one or more of the above-referencedranges (e.g., that further comprises other, different biocides or thatlacks other, different biocides) and/or the total amount of biocide in abinder composition may be in one or more of the above-referenced ranges.

In some embodiments, a binder composition comprises one or morehumectants. Non-limiting examples of suitable humectants includealcohols (e.g., mono- or multifunctional alcohols), ethers, lactones,lactams (e.g., substituted lactams, unsubstituted lactams), amides,amines, sulfones, sulfoxides, sulfides, carbonates, and carbamates.Further non-limiting examples of suitable humectants include1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol,1,5-pentanediol, 1,6-hexanediol, 1,2-hexanediol, 1,8-octanediol,1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,ethylene glycol, diethylene glycol, triethylene glycol, tetraethyleneglycol, poly(ethylene glycol) having a weight average molecular weightof less than 2000 Da, dipropylene glycol, propylene glycol,polypropylene glycol having weight average molecular weight less than2000, glycerol, 1,2,6-hexanetriol, sorbitol, 2-pyrrolidone,1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, N-ethylacetamide,N-methlpropionamide, N-acetyl ethanolamine, N-methylacetamide,formamide, 3-amino-1,2-propanediol, 2,2-thiodiethanol,3,3-thiodipropanol, tetramethylene sulfone, butadiene sulfone, ethylenecarbonate, butyrolacetone, tetrahydrofurfuryl alcohol, glycerol,1,2,4-butenetriol, trimethylpropane, pantothenol, urea, biuret,triethanolamine, and diethanolamine.

In some embodiments, a binder composition comprises a humectant orcombination of humectants that makes up less than or equal to 30 wt %,less than or equal to 25 wt %, less than or equal to 20 wt %, less thanor equal to 17.5 wt %, less than or equal to 15 wt %, less than or equalto 12.5 wt %, less than or equal to 10 wt %, less than or equal to 7.5wt %, less than or equal to 5 wt %, less than or equal to 2.5 wt %, orless than or equal to 1 wt % of the binder composition. In someembodiments, a binder composition comprises a humectant or combinationof humectants that makes up greater than or equal to 0 wt %, greaterthan or equal to 1 wt %, greater than or equal to 2.5 wt %, greater thanor equal to 5 wt %, greater than or equal to 7.5 wt %, greater than orequal to 10 wt %, greater than or equal to 12.5 wt %, greater than orequal to 15 wt %, greater than or equal to 17.5 wt %, greater than orequal to 20 wt %, or greater than or equal to 25 wt % of the bindercomposition. Combinations of the above-referenced ranges are alsopossible (e.g., less than or equal to 30 wt % and greater than or equalto 0 wt %). Other ranges are also possible. It should also be understoodthat a single humectant may be present in a binder composition in one ormore of the above-referenced ranges (e.g., that further comprises other,different humectants or that lacks other, different humectants) and/orthe total amount of humectant in a binder composition may be in one ormore of the above-referenced ranges.

As described above, in some embodiments, a binder composition isprovided in a container configured to resist corrosion by the bindercomposition. For example, the container may comprise acorrosion-resistant material arranged within the container. Thecontainer may be designed such that any binder material it contains isonly in contact with the corrosion-resistant material during long termstorage (e.g., the corrosion-resistant material may cover the innerportions of the container that would be exposed to the bindercomposition when the container is sealed and/or stored). In someembodiments, the container is designed such that any binder material itcontains or dispenses is only in contact with the corrosion-resistantmaterial (e.g., the corrosion-resistant material may cover all portionsof the container which the binder composition is configured to contactduring storage thereof and dispensing thereof). The container mayfurther comprise a material that is not corrosion-resistant. Thismaterial may be positioned in portions of the container with which thebinder is not in contact during storage and/or dispensing.

FIG. 8A shows one non-limiting embodiment of a container configured toresist corrosion by a binder composition. In FIG. 8A, a container 800comprises a corrosion-resistant material 810 arranged within thecontainer. The container 800 also comprises a material 820 that is notcorrosion-resistant material and on which the corrosion-resistantmaterial is disposed. In some embodiments, like the embodiment shown inFIG. 8B, a container like that shown in FIG. 8A may contain and/or beconfigured to contain a binder composition. In FIG. 8B, a container 802comprises a binder composition 832. The binder composition may be acomposition that is not corrosive to the corrosion-resistant material812 with which it is in contact and/or may be a composition that iscorrosive to the material 822 on which the corrosion-resistant material812 is disposed.

In some embodiments, a container comprising a corrosion-resistantmaterial arranged therein is one part of an article for supplying abinder composition to an additive manufacturing system. The article mayfurther comprise one or more additional components. For instance, thearticle may comprise an interfacing component configured to interfacewith an additive manufacturing system. The interfacing component may beconfigured to do so by removably engaging with the additivemanufacturing printing system. By way of example, the interfacingcomponent may comprise one or more portions that can be reversiblyattached to the additive manufacturing system, such as a barbed fittingand/or tubing. In some embodiments, an interfacing component may also becoupled to the container. The coupling may be permanent (e.g., theinterfacing component may be integrally connected to the containerand/or may require specialized tools to be removed from the container)or may be reversible (e.g., the interfacing component may be coupled tothe container by a barbed fitting and/or tubing). FIG. 8C shows onenon-limiting example of an article 1004 for supplying a bindercomposition to an on-demand printing system comprising a container 804and an interfacing component 904.

Portions of articles for supplying a binder composition to an on-demandprinting system may comprise a variety of suitable materials. Forinstance, in some embodiments, a corrosion-resistant material arrangedtherein may comprise poly(ethylene) and/or an epoxy phenolic polymer. Acontainer in which the corrosion-resistant material is arranged maycomprise a metal, such as steel.

As described above, some embodiments relate to metal-based compositestructures comprising a metal powder and some embodiments relate tomethods of forming such structures. Further details regarding such metalpowders are provided below.

In some embodiments, a metal powder comprises a plurality of particleshaving a chemical composition that results in the formation of metalobjects having a desirable chemical composition. For instance, the metalpowder may comprise a plurality of particles comprising a material thatit is desirable for a metal object to comprise and/or be formed from.

In some embodiments, a metal powder comprises a plurality of metalparticles (i.e., a plurality of particles comprising a metal alloy).Non-limiting examples of suitable metal alloys include ferric alloys,such as steels. Non-limiting examples of steels include stainless steels(e.g., 17-4 PH stainless steel, 316 stainless steel, 260L stainlesssteel) and low alloy steels (e.g., 4140 low alloy steel, H13 low alloysteel).

In some embodiments, a metal powder comprises a plurality of particlescomprising a metal alloy comprising chromium (e.g., an alloy comprisingiron and chromium). Chromium may make up greater than or equal to 0 wt%, greater than or equal to 0.1 wt %, greater than or equal to 0.2 wt %,greater than or equal to 0.5 wt %, greater than or equal to 0.8 wt %,greater than or equal to 0.9 wt %, greater than or equal to 1 wt %,greater than or equal to 1.25 wt %, greater than or equal to 1.5 wt %,greater than or equal to 1.75 wt %, greater than or equal to 2 wt %,greater than or equal to 5 wt %, greater than or equal to 7.5 wt %,greater than or equal to 10 wt %, greater than or equal to 12.5 wt %, orgreater than or equal to 15 wt % of the metal alloy. Chromium may makeup less than or equal to 17.5 wt %, less than or equal to 15 wt %, lessthan or equal to 12.5 wt %, less than or equal to 10 wt %, less than orequal to 7.5 wt %, less than or equal to 5 wt %, less than or equal to 2wt %, less than or equal to 1.75 wt %, less than or equal to 2.5 wt %,less than or equal to 1.25 wt %, less than or equal to 1 wt %, less thanor equal to 0.9 wt %, less than or equal to 0.8 wt %, less than or equalto 0.5 wt %, less than or equal to 0.2 wt %, or less than or equal to0.1 wt % of the metal alloy. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0 wt % and less thanor equal to 17.5 wt %, greater than or equal to 0.8 wt % and less thanor equal to 17.5 wt %, greater than or equal to 0.8 wt % and less thanor equal to 1.1 wt %, or greater than or equal to 15 wt % and less thanor equal to 17.5 wt %). Other ranges are also possible. The chromiumcontent of a metal alloy may be determined in accordance with ASTME1086-08.

In some embodiments, a metal powder comprises a plurality of particlescomprising a metal alloy comprising carbon (e.g., an alloy comprisingiron and carbon). Carbon may make up greater than or equal to 0 wt %,greater than or equal to 0.01 wt %, greater than or equal to 0.02 wt %,greater than or equal to 0.03 wt %, greater than or equal to 0.05 wt %,greater than or equal to 0.07 wt %, greater than or equal to 0.1 wt %,greater than or equal to 0.15 wt %, greater than or equal to 0.2 wt %,greater than or equal to 0.25 wt %, greater than or equal to 0.3 wt %,greater than or equal to 0.35 wt %, greater than or equal to 0.38 wt %,or greater than or equal to 0.39 wt % of the metal alloy. Carbon maymake up less than or equal to 0.4 wt %, less than or equal to 0.39 wt %,less than or equal to 0.38 wt %, less than or equal to 0.35 wt %, lessthan or equal to 0.3 wt %, less than or equal to 0.25 wt %, less than orequal to 0.2 wt %, less than or equal to 0.15 wt %, less than or equalto 0.1 wt %, less than or equal to 0.07 wt %, less than or equal to 0.05wt %, less than or equal to 0.03 wt %, less than or equal to 0.02 wt %,or less than or equal to 0.01 wt % of the metal alloy. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 0 wt % and less than or equal to 0.4 wt %, greater than orequal to 0 wt % and less or equal to 0.07 wt %, or greater than or equalto 0.38 wt % and less than or equal to 0.4 wt %). Other ranges are alsopossible. The carbon content of a metal alloy may be determined inaccordance with ASTM E1086-08.

Further examples of elements that may be included in metal alloyssuitable for use in the metal powders described herein include, but arenot limited to, aluminum (which may make up, e.g., greater than or equalto 0.95 wt % and less than or equal to 1.30 wt % of the metal alloy),boron (which may make up, e.g., greater than or equal to 0.001 wt % andless than or equal to 0.003 wt % of the metal alloy), cobalt (which maymake up, e.g., greater than or equal to 0 wt % and less than or equal to8 wt % of the metal alloy), copper (which may make up, e.g., greaterthan or equal to 0 wt % and less than or equal to 5 wt % of the metalalloy), manganese (which may make up, e.g., greater than or equal to 0wt % and less than or equal to 12 wt % of the metal alloy), molybdenum(which may make up, e.g., greater than or equal to 0.2 wt % and lessthan or equal to 5 wt % of the metal alloy), nickel (which may make up,e.g., greater than or equal to 2 wt % and less than or equal to 20 wt %of the metal alloy), phosphorus (which may be present in trace amountsand/or make up, e.g., greater than or equal to 0 wt % and less than orequal to 0.05 wt % of the metal alloy), silicon (which may make up,e.g., greater than or equal to 0.2 wt % and less than or equal to 2 wt %of the metal alloy), vanadium (which may make up, e.g., greater than orequal to 0 wt % and less than or equal to 5 wt % of the metal alloy),tungsten (which may make up, e.g., greater than or equal to 0 wt % andless than or equal to 18 wt % of the metal alloy), and zirconium (whichmay make up, e.g., approximately 0.1 wt % of the metal alloy). Theamount of each of the above-referenced elements in a metal alloy may bedetermined in accordance with ASTM E1086-08.

The metal powders described herein may comprise a plurality of metalparticles have a variety of suitable sizes. In some embodiments, a metalpowder may comprise a plurality of particles having a size suitable forthe formation of metal objects by additive manufacturing methods (e.g.,that have good flow behavior and/or are suitable for sintering). Forinstance, the plurality of particles may have an advantageous value ofD50 (i.e., an advantageous median particle size). In some embodiments,the plurality of particles has a D50 of greater than or equal to 5microns, greater than or equal to 7 microns, greater than or equal to 10microns, greater than or equal to 12.5 microns, greater than or equal to15 microns, greater than or equal to 20 microns, greater than or equalto 25 microns, greater than or equal to 30 microns, greater than orequal to 35 microns, greater than or equal to 40 microns, or greaterthan or equal to 45 microns. In some embodiments, the plurality ofparticles has a D50 of less than or equal to 50 microns, less than orequal to 45 microns, less than or equal to 40 microns, less than orequal to 35 microns, less than or equal to 30 microns, less than orequal to 25 microns, less than or equal to 20 microns, less than orequal to 15 microns, less than or equal to 12.5 microns, less than orequal to 10 microns, or less than or equal to 7 microns. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 5 microns and less than or equal to 50 microns, or greater thanor equal to 7 microns and less than or equal to 20 microns). Otherranges are also possible. The D50 of a plurality of particles may bedetermined in accordance with ASTM E2651-13.

As described above, certain embodiments relate to methods of additivemanufacturing by binder jet printing. Further details regarding suchembodiments and the articles produced by methods of additivemanufacturing are provided below.

As also described above, some methods of additive manufacturing comprisedepositing a binder composition on a layer of metal powder. The layer ofmetal powder may be a layer that comprises a plurality of particles thatare not adhered together. For instance, the metal particles in a layerof metal powder may be readily separated from each other by theapplication of minimal amounts of force, such as the application offorces present during typical processes of depositing a layer of metalpowder and/or the application of gravity.

When present, layers of metal powder may have a variety of suitablethicknesses. In some embodiments, a layer of metal powder has athickness of greater than or equal to 25 microns, greater than or equalto 30 microns, greater than or equal to 35 microns, greater than orequal to 40 microns, greater than or equal to 45 microns, greater thanor equal to 50 microns, greater than or equal to 60 microns, greaterthan or equal to 70 microns, greater than or equal to 80 microns, orgreater than or equal to 90 microns. In some embodiments, a layer ofmetal powder has a thickness of less than or equal to 100 microns, lessthan or equal to 90 microns, less than or equal to 80 microns, less thanor equal to 70 microns, less than or equal to 60 microns, less than orequal to 50 microns, less than or equal to 45 microns, less than orequal to 40 microns, less than or equal to 35 microns, or less than orequal to 30 microns. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 25 microns and less thanor equal to 100 microns). Other ranges are also possible.

Once a layer of metal powder has been deposited, deposition of a bindercomposition thereon may occur (e.g., by means of a print head, such asan ink jet print head, that ejects a plurality of droplets) at a varietyof suitable velocities. In some embodiments, the binder composition isdeposited at a velocity of greater than or equal to 3 m/s, greater thanor equal to 4 m/s, greater than or equal to 5 m/s, greater than or equalto 6 m/s, greater than or equal to 7 m/s, greater than or equal to 8m/s, greater than or equal to 9 m/s, greater than or equal to 10 m/s, orgreater than or equal to 11 m/s. In some embodiments, the bindercomposition is deposited at a velocity of less than or equal to 12 m/s,less than or equal to 11 m/s, less than or equal to 10 m/s, less than orequal to 9 m/s, less than or equal to 8 m/s, less than or equal to 7m/s, less than or equal to 6 m/s, less than or equal to 5 m/s, or lessthan or equal to 4 m/s. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 3 m/s and less than orequal to 12 m/s greater than or equal to 6 m/s and less than or equal to12 m/s). Other ranges are also possible. Binder composition velocity maybe measured using a high speed camera, or a stroboscope/cameraapparatus, with imaging software as described in the Examples. Thevelocity may be measured when droplets of the binder composition are 0.5mm from the orifice of the print head from which they are ejected.

In some embodiments, a binder composition is deposited in the form ofdroplets. For instance, in some embodiments, a step of depositing abinder composition on layer of metal powder comprises producing adroplet of the binder composition and depositing the droplet of thebinder composition on the layer of metal powder. When produced, dropletsmay have a variety of suitable volumes. In some embodiments, a methodcomprises producing a droplet having a volume of greater than or equalto 0.5 pL, greater than or equal to 0.75 pL, greater than or equal to 1pL, greater than or equal to 1.5 pL, greater than or equal to 2 pL,greater than or equal to 3 pL, greater than or equal to 5 pL, greaterthan or equal to 7.5 pL, greater than or equal to 10 pL, greater than orequal to 12 pL, greater than or equal to 15 pL, greater than or equal to20 pL, greater than or equal to 25 pL, greater than or equal to 30 pL,or greater than or equal to 35 pL. In some embodiments, a methodcomprises producing a droplet having a volume of less than or equal to40 pL, less than or equal to 35 pL, less than or equal to 30 pL, lessthan or equal to 25 pL, 20 pL, less than or equal to 15 pL, less than orequal to 12 pL, less than or equal to 10 pL, less than or equal to 7.5pL, less than or equal to 5 pL, less than or equal to 3 pL, less than orequal to 2 pL, less than or equal to 1.5 pL, less than or equal to 1 pL,or less than or equal to 0.75 pL. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 0.5 pL and lessthan or equal to 40 pL, greater than or equal to 0.5 pL and less than orequal to 20 pL, greater than or equal to 0.5 pL and less than or equalto 2 pL, greater than or equal to 2 pL and less than or equal to 20 pL,or greater than or equal to 2 pL and less than or equal to 12 pL). Otherranges are also possible. Droplet volume may be measured using a highspeed camera, or a stroboscope/camera apparatus, with imaging softwareas described in the examples. It should also be understood that somemethods may comprise producing a plurality of droplets comprising one ormore droplets having a volume in one or more of the above-referencedranges and that some methods may comprise producing a plurality ofdroplets having an average volume in one or more of the above-referencedranges.

In some embodiments in which a plurality of droplets of a bindercomposition are produced, they may be produced in a manner such thatthey have a relatively uniform volume. Production of droplets withrelatively uniform volumes may enhance the precision with which featuresin a composite layer can be formed, as it may allow more control overthe amount and location of the binder composition in the composite layerby reducing the amount of unwanted droplets and/or droplets of unwantedvolumes. Volume uniformity may enhance control over the volumetric ratioof the binder composition to the metal powder on which it is deposited,which may promote better control over the properties of the metal objectfabricated therefrom.

In some embodiments, a plurality of droplets comprises almostexclusively main droplets and very few satellite droplets. In otherwords, the binder composition may form droplets in a manner that doesnot substantially form satellite droplets. The satellite droplets may bedroplets having a smaller volume than the main droplets. In someembodiments, satellite droplets have a volume of less than or equal to1.5 pL, less than or equal to 1 pL, or less than or equal to 0.5 pL. Forinstance, in some embodiments, less than 1% of the droplets within aplurality of droplets are satellite droplets (e.g., less than 1% of thedroplets have a volume of less than or equal to 1.5 pL, less than orequal to 1 pL, or less than or equal to 0.5 pL when the main dropletshave a volume of greater than or equal to 0.5 pL, greater than or equalto 1 pL, or greater than or equal to 1.5 pL). In some embodiments, aplurality of droplets comprises exclusively main droplets and nosatellite droplets and/or a binder formulation forms droplets in amanner that does not form satellite droplets. The presence of satellitedroplets, and their amount, may be determined by using the techniquedescribed for measuring droplet volume described above.

Droplets of a binder composition may be produced in a variety ofsuitable manners. In some embodiments, one or more droplets of a bindercomposition are produced by a print head, such as a piezoelectric printhead or a thermal print head. Without wishing to be bound by anyparticular theory, it is believed that piezoelectric print heads may beconfigured to form larger droplets comprising a binder composition thanthermal print heads (e.g., piezoelectric print heads may be configuredto form droplets having volumes of greater than or equal to 2 pL andless than or equal to 20 pL, while thermal print heads may be configuredto form droplets having volumes of greater than or equal to 0.5 pL andless than or equal to 2 pL). Non-limiting examples of suitable printheads include SAMBA (FujiFilm Co.), SG-1024 (Fujifilm Co.), XAAR 5601(XAAR, plc), VersaPass (Memjet), Duralink (Memjet), and Duraflex(Memjet).

As described above, certain embodiments relate to three-dimensionalcompositions. The three-dimensional compositions may include a metalpowder and a binder composition. The binder composition may comprise oneor more of the components described elsewhere herein with respect tobinder compositions (e.g., water, a polymer including an acrylic acidrepeat unit, a cross-linking agent, and/or a pH modifier).

As described above, certain embodiments relate to the drying and/orcross-linking of a binder composition and certain embodiments relate tometal-based composite structures formed by the drying and/orcross-linking of a binder composition positioned in a three-dimensionalcomposition. Further details regarding such embodiments are providedbelow.

As also described above, the drying and/or cross-linking of a bindercomposition may be accomplished by exposing the binder composition to astimulus that is heat. The temperature to which the binder compositionis heated may be sufficient to dry and/or cross-link the bindercomposition without appreciably degrading the portion(s) of the bindercomposition, if any, configured to remain in the metal-based compositestructure during this step (e.g., a polymer). In some embodiments,drying and/or cross-linking a binder composition comprises heating anenvironment in which a three-dimensional composition is positioned to atemperature of greater than or equal to 90° C., greater than or equal to100° C., greater than or equal to 110° C., greater than or equal to 120°C., greater than or equal to 130° C., greater than or equal to 140° C.,greater than or equal to 150° C., greater than or equal to 160° C.,greater than or equal to 170° C., greater than or equal to 180° C.,greater than or equal to 190° C., greater than or equal to 200° C.,greater than or equal to 210° C., greater than or equal to 220° C.,greater than or equal to 230° C., or greater than or equal to 240° C. Insome embodiments, drying and/or cross-linking a binder compositioncomprises heating an environment in which the three-dimensionalcomposition is positioned to a temperature of less than or equal to 250°C., less than or equal to 240° C., less than or equal to 230° C., lessthan or equal to 220° C., less than or equal to 210° C., less than orequal to 200° C., less than or equal to 190° C., less than or equal to180° C., less than or equal to 170° C., less than or equal to 160° C.,less than or equal to 150° C., less than or equal to 140° C., less thanor equal to 130° C., less than or equal to 120° C., or less than orequal to 100° C. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 90° C. and less than or equalto 250° C., greater than or equal to 120° C. and less than or equal to220° C.). Other temperatures are also possible. The temperature of anenvironment may be determined by use of a thermocouple positioned in theenvironment.

Non-limiting examples of suitable environments in which athree-dimensional composition may be positioned during drying and/orheating of the binder composition include an oven, a furnace, a powderbed. The relevant environment may comprise a variety of suitable typesof gases. By way of example, the relevant environment may comprise air,may comprise hydrogen, and/or may comprise an inert gas (e.g., nitrogen,argon). In some embodiments, the relevant environment may lack speciesthat are reactive at the temperature to which the environment is heated.By way of example, the relevant environment may be an inert environment(e.g., it may comprise, consist essentially of, and/or consist of aninert gas such as nitrogen and/or argon). The pressure of the relevantenvironment may generally be selected as desired. Some relevantenvironments may be at atmospheric pressure; some may be at a pressureless than atmospheric pressure.

Drying and/or heating a three-dimensional composition may be performedfor a variety of suitable amounts of time. The time may be selected toprovide a desired level of drying and/or cross-linking of the bindercomposition. By way of example, if a light level of drying and/orcross-linking is desired, a drying and/or cross-linking step may beperformed for a relatively short time. Similarly, if a relatively highlevel of drying and/or cross-linking is desired, a drying and/orcross-linking step may be performed for a relatively long time. In someembodiments, a drying and/or cross-linking step comprises heating anenvironment in which a three-dimensional composition is positioned for atime period of greater than or equal to 15 minutes, greater than orequal to 30 minutes, greater than or equal to 45 minutes, greater thanor equal to 1 hour, greater than or equal to 90 minutes, greater than orequal to 2 hours, greater than or equal to 3 hours, greater than orequal to 4 hours, greater than or equal to 5 hours, greater than orequal to 6 hours, greater than or equal to 8 hours, greater than orequal to 10 hours, greater than or equal to 12 hours, greater than orequal to 14 hours, greater than or equal to 16 hours, greater than orequal to 18 hours, greater than or equal to 20 hours, greater than orequal to 1 day, greater than or equal to 2 days, greater than or equalto 3 days, greater than or equal to 4 days, greater than or equal to 100hours, greater than or equal to 5 days, or greater than or equal to 6days. In some embodiments, a drying and/or cross-linking step comprisesheating an environment in which a three-dimensional composition ispositioned for a time period of less than or equal to 1 week, less thanor equal to 6 days, less than or equal to 5 days, less than or equal to100 hours, less than or equal to 4 days, less than or equal to 3 days,less than or equal to 2 days, less than or equal to 1 day, less than orequal to 20 hours, less than or equal to 18 hours, less than or equal to16 hours, less than or equal to 14 hours, less than or equal to 12hours, less than or equal to 10 hours, less than or equal to 8 hours,less than or equal to 6 hours, less than or equal to 5 hours, less thanor equal to 4 hours, less than or equal to 3 hours, less than or equalto 140 minutes, less than or equal to 120 minutes, or less than or equalto 100 minutes. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 15 minutes and less than orequal to 6 days, greater than or equal to 15 minutes and less than orequal to 120 minutes, or greater than or equal to 45 minutes and lessthan or equal to 120 minutes). Other ranges are also possible.

In some embodiments, drying and/or heating a three-dimensionalcomposition comprises heating the environment in which thethree-dimensional composition is positioned to one temperature in one ormore of the above-referenced ranges and holding the temperature of theenvironment thereat for an amount of time in one of the above-referencedranges. In some embodiments, drying and/or heating a three-dimensionalcomposition comprises heating an environment in which thethree-dimensional composition is positioned to two or more temperaturesin the above-referenced ranges sequentially and holding the temperatureof the environment at each of the two or more temperatures. In suchembodiments, the relevant environment may be held at each of therelevant temperatures for a period of time in one or more of theabove-referenced ranges and/or may be heated such that the total time itis held at all of the relevant temperatures is in one or more of theabove-referenced ranges.

In some embodiments, drying and/or heating a three-dimensionalcomposition is performed in a manner that minimizes the tendency of thethree-dimensional object to form cracks. For instance, drying and/orheating a three-dimensional composition may be performed in a mannersuch that changes between temperatures are performed relatively slowly.In some embodiments, drying and/or heating a three-dimensionalcomposition is performed such that the change in temperature of theenvironment in which the three-dimensional object is positioned is lessthan or equal to 2° C./min, less than or equal to 1.5° C./min, less thanor equal to 1° C./min, at less than or equal to 0.75° C./min, less thanor equal to 0.5° C./min, or less than or equal to 0.25° C./min. In someembodiments, drying and/or heating a three-dimensional composition isperformed such that that the change in temperature of the environment inwhich the three-dimensional composition is positioned is greater than orequal to 0.1° C./min, greater than or equal to 0.25° C./min, greaterthan or equal to 0.5° C./min, greater than or equal to 0.75° C./min,greater than or equal to 1° C./min, greater than or equal to 1.5°C./min. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 2° C./min and less than or equal to 0.1°C./min). Other ranges are also possible. In some embodiments, thetemperature of the environment in which the three-dimensionalcomposition is positioned is either constant or changes at a rate in oneor more of the ranges described above throughout a drying and/orcross-linking process. In some embodiments, a drying and/orcross-linking process comprises a change in temperature at a rate in oneor more of the ranges described above but also comprises further changesin temperature (e.g., at a rate in one or more of the ranges describedabove, at a rate outside of the ranges described above).

As described above, certain embodiments relate to metal-based compositestructures. Further details regarding such embodiments are providedbelow.

In some embodiments, a metal-based composite structure is provided. Themetal-based composite structure may comprise a metal powder, one or morecomponents of a binder composition (e.g., a polymer including an acrylicacid repeat unit, a cross-linking agent), and/or one or more reactionproducts of one or more components of a binder composition (e.g., across-linked polymer formed by a reaction of a polymer present in thebinder composition with a cross-linking agent present in the bindercomposition). The components of the binder composition and the reactionproducts thereof may together form a binder. In some embodiments, themetal powder comprises a plurality of particles is embedded in thebinder. For instance, the binder may form a matrix in which theplurality of particles is disposed. As another example, the binder maycoat the surfaces of the particles within the plurality of particlesand/or the particles within the plurality of particles may be intopological contact with each other through the binder.

In some embodiments, a metal-based composite structure comprises abinder. For instance, the binder may adhere to particles positioned inthe composite layer and may have sufficient cohesive strength to form aself-supporting structure in which the particles are embedded.

A metal powder present in a metal-based composite structure may make upany suitable amount thereof. In some embodiments, the metal powder makesup greater than or equal to 92 wt %, greater than or equal to 93 wt %,greater than or equal to 94 wt %, greater than or equal to 95 wt %,greater than or equal to 96 wt %, greater than or equal to 97 wt %,greater than or equal to 98 wt %, greater than or equal to 99 wt %, orgreater than or equal to 99.5 wt % of the metal-based compositestructure. In some embodiments, the metal powder makes up less than orequal to 99.9 wt %, less than or equal to 99.5 wt %, less than or equalto 99 wt %, less than or equal to 98 wt %, less than or equal to 97 wt%, less than or equal to 96 wt %, less than or equal to 95 wt %, lessthan or equal to 94 wt %, or less than or equal to 93 wt % of themetal-based composite structure. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 92 wt % andless than or equal to 99.9 wt %, or greater than or equal to 96 wt % andless than or equal to 99.9 wt %). Other ranges are also possible.

The metal-based composite structures described herein may haveadvantageously have relatively high transverse flexural strengths.Desirably, high values of transverse flexural strength may reduce thetendency of metal-based composite structures to fail during furtheradditive manufacturing steps. In some embodiments, a metal-basedcomposite structure has a transverse flexural strength of greater thanor equal to 1 MPa, greater than or equal to 2 MPa, greater than or equalto 5 MPa, greater than or equal to 7.5 MPa, greater than or equal to 10MPa, greater than or equal to 20 MPa, greater than or equal to 50 MPa,greater than or equal to 75 MPa, greater than or equal to 100 MPa, orgreater than or equal to 125 MPa. In some embodiments, a metal-basedcomposite structure has a transverse flexural strength of less than orequal to 150 MPa, less than or equal to 125 MPa, less than or equal to100 MPa, less than or equal to 75 MPa, less than or equal to 50 MPa,less than or equal to 20 MPa, less than or equal to 10 MPa, less than orequal to 7.5 MPa, less than or equal to 5 MPa, or less than or equal to2 MPa. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 1 MPa and less than or equal to 150 MPa,or greater than or equal to 2 MPa and less than or equal to 150 MPa).Other ranges are also possible.

The transverse flexural strength of a metal-based composite structuremay be the transverse flexural strength as determined by the three-pointbending test described in ASTM B312-14 and/or may be the transverseflexural strength as determined by the four-point bending test describedin ASTM C1161-18. In other words, some metal-based composite structuresmay have transverse flexural strengths as determined by the three-pointbending test described in ASTM B312-14 in one or more of theabove-referenced ranges, some metal-based composite structures may havetransverse flexural strengths as determined by the four-point bendingtest described in ASTM C1161-18 in one or more of the above-referencedranges, and some metal-based composite structures may have transverseflexural strengths as determined by the three-point bending testdescribed in ASTM B312-14 and as determined the four-point bending testdescribed in ASTM C1161-18 in one or more of the above-referencedranges.

As described above, certain embodiments relate to heating metal-basedcomposite structures. Certain embodiments relate to de-bound metalstructures formed by heating metal-based composite structures. Furtherdetails regarding such embodiments are provided below.

During this heating process, it may be desirable for the binder and/orbinder composition to be removed from the metal-based compositestructure. Accordingly, a temperature is typically selected thatpromotes volatilization (e.g., evaporation, thermal decomposition and/ordegradation) of the binder and/or binder composition.

In some embodiments, an environment in which a metal-based compositestructure is positioned is heated to a temperature of greater than orequal to 200° C., greater than or equal to 210° C., greater than orequal to 220° C., greater than or equal to 230° C., greater than orequal to 240° C., greater than or equal to 250° C., greater than orequal to 275° C., greater than or equal to 300° C., greater than orequal to 350° C., greater than or equal to 400° C., greater than orequal to 450° C., greater than or equal to 500° C., greater than orequal to 550° C., greater than or equal to 600° C., or greater than orequal to 650° C. In some embodiments, an environment in which ametal-based composite structure is positioned is heated to a temperatureof less than or equal to 700° C., less than or equal to 650° C., lessthan or equal to 600° C., less than or equal to 550° C., less than orequal to 500° C., less than or equal to 400° C., less than or equal to350° C., less than or equal to 300° C., less than or equal to 275° C.,less than or equal to 250° C., less than or equal to 240° C., less thanor equal to 230° C., less than or equal to 220° C., or less than orequal to 210° C. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 200° C. and less than or equalto 700° C.). Other ranges are also possible. The temperature of anenvironment may be determined by use of a thermocouple positioned in theenvironment.

It should be understood that some heating steps may comprise heating ametal-based composite structure to two or more temperatures in sequence.For instance, a heating step may comprise heating a metal-basedcomposite structure to one temperature at which one portion of thebinder is expected to degrade (e.g., based on a thermogravimetricanalysis performed on the binder) and then heating the metal-basedcomposite structure to another temperature at which another portion ofthe binder is expected to degrade (e.g., based on a thermogravimetricanalysis performed on the binder). These temperatures may besuccessively increasing (e.g., each temperature to which the metal-basedcomposite structure is heated during the heating step may be higher thanthe previous temperature to which the metal-based composite structurewas heated during the heating step). Some such heating steps maycomprise heating the metal-based composite structure to three, four,five, or even more temperatures in sequence. Some or all of thetemperatures may be within one or more of the above-described ranges.

In some embodiments, a heating step is performed in a manner thatminimizes the tendency of the metal-based composite structure to formcracks. For instance, the heating step may be performed in a manner suchthat changes between temperatures are accomplished relatively slowly. Insome embodiments, a heating step is performed such that the change intemperature of the environment in which the metal-based compositestructure is positioned is less than or equal to 2° C./min, less than orequal to 1.5° C./min, less than or equal to 1° C./min, less than orequal to 0.75° C./min, less than or equal to 0.5° C./min, or less thanor equal to 0.25° C./min. In some embodiments, a heating step isperformed such that that the change in temperature of the environment inwhich the metal-based composite structure is positioned is greater thanor equal to 0.1° C./min, greater than or equal to 0.25° C./min, greaterthan or equal to 0.5° C./min, greater than or equal to 0.75° C./min,greater than or equal to 1° C./min, or greater than or equal to 1.5°C./min. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 2° C./min and less than or equal to 0.1°C./min). Other ranges are also possible. In some embodiments, thetemperature of the environment in which the metal-based compositestructure is positioned is either constant or changes at a rate in oneor more of the ranges described above throughout the heating step. Insome embodiments, the heating step comprises a change in temperature ata rate in one or more of the ranges described above but also comprisesfurther changes in temperature (e.g., at a rate in one or more of theranges described above, at a rate outside of the ranges describedabove).

A metal-based composite structure may be heated for a variety ofsuitable amounts of time. In some embodiments, an environment in which ametal-based composite material is positioned is heated for a time periodof greater than or equal to 15 minutes, greater than or equal to 30minutes, greater than or equal to 45 minutes, greater than or equal to60 minutes, greater than or equal to 100 minutes, greater than or equalto 120 minutes, greater than or equal to 140 minutes, greater than orequal to 2 hours, greater than or equal to 3 hours, greater than orequal to 4 hours, greater than or equal to 4.5 hours, greater than orequal to 5 hours, greater than or equal to 5.5 hours, greater than orequal to 6 hours, greater than or equal to 6.5 hours, greater than orequal to 7 hours, greater than or equal to 7.5 hours, greater than orequal to 8 hours, greater than or equal to 8.5 hours, greater than orequal to 9 hours, greater than or equal to 9.5 hours, greater than orequal to 10 hours, greater than or equal to 12 hours, greater than orequal to 12 hours, greater than or equal to 14 hours, greater than orequal to 18 hours, greater than or equal to 1 day, greater than or equalto 2 days, greater than or equal to 3 days, greater than or equal to 4days, greater than or equal to 5 days, or greater than or equal to 6days. In some embodiments, an environment in which a metal-basedcomposite material is positioned is heated for a time period of lessthan or equal to 1 week, less than or equal to 6 days, less than orequal to 5 days, less than or equal to 4 days, less than or equal to 3days, less than or equal to 2 days, less than or equal to 1 day, lessthan or equal to 18 hours, less than or equal to 14 hours, less than orequal to 12 hours, less than or equal to 10 hours, less than or equal to9.5 hours, less than or equal to 9 hours, less than or equal to 8.5hours, less than or equal to 8 hours, less than or equal to 7.5 hours,less than or equal to 7 hours, less than or equal to 6.5 hours, lessthan or equal to 6 hours, less than or equal to 5.5 hours, less than orequal to 5 hours, less than or equal to 4.5 hours, less than or equal to3 hours, less than or equal to 2 hours, less than or equal to 140minutes, less than or equal to 120 minutes, or less than or equal to 100minutes. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 15 minutes and less than or equal to 1week, greater than or equal to 15 minutes and less than or equal to 1day, or greater than or equal to 4 hours and less than or equal to 10hours). Other ranges are also possible.

In some embodiments, heating a metal-based composite material comprisesheating the environment in which the metal-based composite material ispositioned to one temperature in one or more of the above-referencedranges and holding the temperature of the environment thereat for anamount of time in one of the above-referenced ranges. In someembodiments, heating a metal-based composite material comprises heatingan environment in which the metal-based composite is positioned to twoor more temperatures in the above-referenced ranges sequentially andholding the temperature of the environment at each of the two or moretemperatures. In such embodiments, the relevant environment may be heldat each of the relevant temperatures for a period of time in one or moreof the above-referenced ranges and/or may be heated such that the totaltime it is held at all of the relevant temperatures is in one or more ofthe above-referenced ranges.

Non-limiting examples of suitable environments in which a metal-basedcomposite structure may be positioned during heating include an oven, afurnace, and a powder bed. In some embodiments, during a heating step,the pressure of the environment to which the metal-based compositestructure is exposed is set to a full vacuum or a partial vacuum toremove decomposition products from the metal-based composite structure.In some embodiments, the pressure is greater than or equal to 10⁻¹¹ bar,greater than or equal to 10⁻¹⁰ bar, greater than or equal to 10⁻⁹ bar,greater than or equal to 10⁻⁸ bar, greater than or equal to 10⁻⁷ bar,greater than or equal to 10⁻⁶ bar, greater than or equal to 10⁻⁵ bar,greater than or equal to 10⁴ bar, greater than or equal to 10⁻³ bar,greater than or equal to 10⁻² bar, greater than or equal to 10⁻¹ bar,greater than or equal to 1 bar, greater than or equal to 10 bar, greaterthan or equal to 20 bar, or greater than or equal to 50 bar. In someembodiments, the pressure is less than or equal to 70 bar, less than orequal to 50 bar, less than or equal to 20 bar, less than or equal to 10bar, less than or equal to 1 bar, less than or equal to 10⁻¹ bar, lessthan or equal to 10⁻² bar, less than or equal to 10⁻³ bar, less than orequal to 10⁴ bar, less than or equal to 10⁻⁵ bar, less than or equal to10⁻⁶ bar, less than or equal to 10⁻⁷ bar, less than or equal to 10⁻⁸bar, less than or equal to 10⁻⁹ bar, or less than or equal to 10⁻¹⁰ bar.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 10⁻¹¹ bar and less than or equal to 70 bar,greater than or equal to 10⁻¹¹ bar and less than or equal to 10⁻³ bar,greater than or equal to 10⁻³ bar and less than or equal to 70 bar,greater than or equal to 10⁻³ bar and less than or equal to 1 bar, orgreater than or equal to 10⁻³ bar and less than or equal to 10⁻¹ bar).Other ranges are also possible. The pressure may be determined by apressure gauge. In some embodiments, the pressure of the environment towhich the metal-based composite structure is exposed is cycled betweenatmospheric pressure and a pressure in one or more of theabove-referenced ranges.

In some embodiments, an environment to which a metal-based compositestructure is exposed during a heating step comprises one or more gases.For instance, in some embodiments, the relevant environment may compriseone or more species that are reactive (e.g., with one or more componentsof the binder) at the temperature to which the environment is heated. Byway of example, the relevant environment may be an oxidative environment(e.g., it may comprise air). As another example, the relevantenvironment may be a reducing environment (e.g., it may comprisehydrogen). In some embodiments, the relevant environment may lackspecies that are reactive at the temperature to which the environment isheated. By way of example, the relevant environment may be an inertenvironment (e.g., it may comprise, consist essentially of, and/orconsist of an inert gas such as argon).

In some embodiments, an environment in which a metal-based compositestructure is positioned during heating comprises a relatively low amountof one or more species (e.g., one or more species reactive with one ormore components of the binder). For instance, in some embodiments, anenvironment in which a metal-based composite structure is heatedcomprises greater than or equal to 2 wt %, greater than or equal to 4 wt%, greater than or equal to 6 wt %, or greater than or equal to 8 wt %hydrogen. The environment in which the metal-based composite structureis heated may comprise less than or equal to 10 wt %, less than or equalto 8 wt %, less than or equal to 6 wt %, or less than or equal to 4 wt %hydrogen. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 2 wt % hydrogen and less than or equalto 10 wt % hydrogen). Other ranges are also possible. For instance, insome embodiments, the environment in which the metal-based compositestructure is heated comprises more than 10 wt % hydrogen (e.g., up to100 wt % hydrogen).

In some embodiments, an environment in which a metal-based compositestructure is heated has an oxygen content of at most 10 ppm, at most 8ppm, at most 6 ppm, at most 4 ppm, at most 2 ppm, or at most 1 ppm. Theenvironment in which a metal-based composite structure is heated mayhave an oxygen content of at least 0 ppm, at least 1 ppm, at least 2ppm, at least 4 ppm, at least 6 ppm, or at least 8 ppm. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 10 ppm and less than or equal to 0 ppm). Other ranges are alsopossible. In other embodiments, the metal-based composite structure maybe heated in an environment comprising more oxygen (e.g., when heated inair).

De-bound metal structures may advantageously include relatively lowlevels of certain elements. For instance, in some embodiments, ade-bound metal structure comprises relatively small amounts of carbonand/or oxygen. As described elsewhere herein, such components may reactundesirably with the metal in the de-bound metal structure duringfurther additive manufacturing steps (e.g., during a sintering step). Byway of example, carbon in a de-bound metal structure may reactundesirably with surface oxides also therein.

In some embodiments, carbon makes up less than or equal to 0.5 wt %,less than or equal to 0.4 wt %, less than or equal to 0.2 wt %, lessthan or equal to 0.1 wt %, less than or equal to 0.05 wt %, or less thanor equal to 0.02 wt % of the de-bound metal structure. In someembodiments, carbon makes up greater than or equal to 0 wt %, greaterthan or equal to 0.02 wt %, greater than or equal to 0.05 wt %, greaterthan or equal to 0.1 wt %, greater than or equal to 0.2 wt %, or greaterthan or equal to 0.4 wt % of the de-bound metal structure. Combinationsof the above-referenced ranges are also possible (e.g., less than orequal to 0.5 wt % and greater than or equal to 0 wt %, or less than orequal to 0.1 wt % and greater than or equal to 0 wt %). Other ranges arealso possible. The amount of carbon in the de-bound metal structure maybe determined in accordance with ASTM E1019.

In some embodiments, oxygen makes up less than or equal to 1.5 wt % orless than or equal to 1 wt % of the de-bound metal structure. The amountof oxygen in the de-bound metal structure may be determined inaccordance with ASTM E1019.

As described above, certain embodiments relate to the formation of metalobjects from de-bound metal structures and/or composite metalstructures. Certain embodiments relate to metal objects. Further detailsregarding such embodiments are provided below.

As also described above, formation of a metal object from a de-boundmetal structure and/or a composite metal structure may comprise heatingthe de-bound metal structure and/or the composite metal structure.During this heating process, it is desirable for the de-bound metalstructure and/or a composite metal structure to undergo sinteringwithout undergoing appreciable melting. In some embodiments, anenvironment in which a de-bound metal structure and/or a composite metalstructure is positioned is heated to a temperature of greater than orequal to 500° C., greater than or equal to 550° C., greater than orequal to 600° C., greater than or equal to 650° C., greater than orequal to 700° C., greater than or equal to 750° C., greater than orequal to 800° C., greater than or equal to 850° C., greater than orequal to 900° C., greater than or equal to 950° C., greater than orequal to 1000° C., greater than or equal to 1050° C., greater than orequal to 1100° C., greater than or equal to 1150° C., greater than orequal to 1200° C., greater than or equal to 1250° C., greater than orequal to 1300° C., greater than or equal to 1350° C., greater than orequal to 1400° C., greater than or equal to 1500° C., or greater than orequal to 1600° C. In some embodiments, an environment in which ade-bound metal structure and/or a composite metal structure ispositioned is heated to a temperature of less than or equal to 1700° C.,less than or equal to 1600° C., less than or equal to 1500° C., lessthan or equal to 1400° C., less than or equal to 1350° C., less than orequal to 1300° C., less than or equal to 1250° C., less than or equal to1200° C., less than or equal to 1150° C., less than or equal to 1100°C., less than or equal to 1050° C., less than or equal to 1000° C., lessthan or equal to 950° C., less than or equal to 900° C., less than orequal to 850° C., less than or equal to 800° C., less than or equal to750° C., less than or equal to 700° C., less than or equal to 650° C.,less than or equal to 600° C., or less than or equal to 550° C.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 500° C. and less than or equal to 1700° C.,greater than or equal to 700° C. and less than or equal to 1400° C.,greater than or equal to 750° C. and less than or equal to 1400° C.,greater than or equal to 750° C. and less than or equal to 1200° C., orgreater than or equal to 750° C. and less than or equal to 850° C.).Other ranges are also possible. The temperature of an environment may bedetermined by use of a thermocouple positioned in the environment.

Formation of a metal object may comprise heating an environment in whicha de-bound metal structure and/or a composite metal structure ispositioned in for a variety of suitable amounts of time. In someembodiments, an environment in which a de-bound metal structure and/or acomposite metal structure is positioned is heated for a time period ofgreater than or equal to 30 minutes, greater than or equal to 1 hour,greater than or equal to 2 hours, greater than or equal to 3 hours,greater than or equal to 6 hours, greater than or equal to 9 hours,greater than or equal to 12 hours, greater than or equal to 18 hours,greater than or equal to 1 day, or greater than or equal to 1.5 days. Insome embodiments, an environment in which a de-bound metal structureand/or a composite metal structure is positioned is heated for a timeperiod of less than or equal to 2 days, less than or equal to 1.5 days,less than or equal to 1 day, less than or equal to 18 hours, less thanor equal to 12 hours, less than or equal to 9 hours, less than or equalto 6 hours, less than or equal to 3 hours, less than or equal to 2hours, or less than or equal to 1 hour. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 30 minutes and less than or equal to 2 days). Other ranges are alsopossible.

In some embodiments, heating a de-bound metal structure and/ormetal-based composite structure comprises heating the environment inwhich the de-bound metal structure and/or metal-based compositestructure is positioned to one temperature in one or more of theabove-referenced ranges and holding the temperature of the environmentthereat for an amount of time in one of the above-referenced ranges. Insome embodiments, heating a de-bound metal structure and/or metal-basedcomposite structure comprises heating an environment in which thede-bound metal structure and/or metal-based composite structure ispositioned to two or more temperatures in the above-referenced rangessequentially and holding the temperature of the environment at each ofthe two or more temperatures. In such embodiments, the relevantenvironment may be held at each of the relevant temperatures for aperiod of time in one or more of the above-referenced ranges and/or maybe heated such that the total time it is held at all of the relevanttemperatures is in one or more of the above-referenced ranges.

Non-limiting examples of suitable environments in which a de-bound partmay be positioned during sintering include an oven or a furnace. Therelevant environment may comprise a variety of suitable types of gases.For instance, in some embodiments, the relevant environment may be areducing environment. By way of example, the relevant requirement maycomprise a reducing species, such as hydrogen (e.g., pure hydrogen, amixture of hydrogen and argon comprising 1 vol % to 6 vol % hydrogen, amixture of hydrogen and argon comprising up to 10 vol % hydrogen). Insome embodiments, the relevant environment is an inert environment. Byway of example, the relevant environment may comprise, consist of,and/or consist essentially of inert gases, such as nitrogen, argon,and/or helium. As another example of a type of environment, in someembodiments, the relevant environment may be a vacuum.

Some metal objects described herein advantageously both comprise a metalalloy and have a density that is relatively close to the density of themetal alloy included therein. Metal objects having this property mayinclude a relatively low amount of internal pores (i.e., pores includedin the bulk of the metal object and not in fluidic communication with anenvironment external to the metal object) and/or may include internalpores that make up a relatively small volume fraction of the metalobject. Low amounts and/or volume fractions of internal pores maydesirably increase the robustness and strength of the metal object.

The relationship between the density of a metal object and the densityof a metal alloy included therein may be parametrized by a relativedensity. As used herein, the relative density may be computed bydividing the bulk density of the metal object by the bulk density of therelevant metal alloy and multiplying by 100%. Accordingly, a relativedensity of 100% would indicate that the metal object has a densityidentical to the bulk metal alloy included therein while a relativedensities of less than 100% would indicate that the metal object has adensity less than the metal alloy included therein. The bulk density ofa metal object may be computed in accordance with ASTM B962-17. Itshould be understood that internal pores would contribute to this volume(because they are entirely enclosed by the outer boundary of the metalobject) while open pores and other features partially enclosed by ametal object would not contribute to this volume.

In some embodiments, a metal object has a relative density of greaterthan or equal to 90%, greater than or equal to 91%, greater than orequal to 92%, greater than or equal to 93%, greater than or equal to94%, greater than or equal to 95%, greater than or equal to 96%, greaterthan or equal to 97%, greater than or equal to 98%, or greater than orequal to 99%. In some embodiments, a metal object has a relative densityof less than or equal to 100%, less than or equal to 99%, less than orequal to 98%, less than or equal to 97%, less than or equal to 96%, lessthan or equal to 95%, less than or equal to 94%, less than or equal to93%, less than or equal to 92%, or less than or equal to 91%.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 90% and less than or equal to 100%). Otherranges are also possible.

Metal objects described herein may have a chemical composition similarto the metal powders from which they were formed. For instance, a metalobject may comprise a metal alloy. Non-limiting examples of suitablemetal alloys include ferric alloys, such as steels. Non-limitingexamples of steels include stainless steels (e.g., 17-4 PH stainlesssteel, 316 stainless steel, 260L stainless steel) and low alloy steels(e.g., 4140 low alloy steel). In some embodiments, a metal objectcomprises a precious metal or precious metal alloy from the preciousmetal powder, such as gold, sterling silver, and/or platinum.Non-limiting examples of suitable metal alloys include argentium silver(e.g., 93.5 wt % or 96 wt % silver alloyed with other metals ormetalloids, such as germanium), yellow gold (e.g., 75 wt % gold, 16 wt %silver, 9 wt % copper), rose gold (e.g., 75 wt % gold, 6 wt % silver, 19wt % copper), and platinum (e.g., Pt850/Ir, Pt900/Ir, Pt950/Ir,Pt950/Ru, Pt850/Co50/Pd100, etc.). In some instances, the weight percentof the precious metal and/or precious metal alloy from the preciousmetal powder in the metal object is greater than or equal to 90 wt %,greater than or equal to 93 wt %, greater than or equal to 95 wt %,greater than or equal to 97 wt %, greater than or equal to 98 wt %,and/or up 99 wt %, up to 99.5 wt %, up to 99.9 wt %, or more.Combinations of these ranges are possible (e.g., a wt % of between 93 wt% and 99 wt %.

In some embodiments, a metal object comprises a metal alloy comprisingchromium (e.g., an alloy comprising iron and chromium). Chromium maymake up greater than or equal to 0 wt %, greater than or equal to 0.1 wt%, greater than or equal to 0.2 wt %, greater than or equal to 0.5 wt %,greater than or equal to 0.8 wt %, greater than or equal to 0.9 wt %,greater than or equal to 1 wt %, greater than or equal to 1.25 wt %,greater than or equal to 1.5 wt %, greater than or equal to 1.75 wt %,greater than or equal to 2 wt %, greater than or equal to 5 wt %,greater than or equal to 7.5 wt %, greater than or equal to 10 wt %,greater than or equal to 12.5 wt %, or greater than or equal to 15 wt %of the metal object. Chromium may make up less than or equal to 17.5 wt%, less than or equal to 15 wt %, less than or equal to 12.5 wt %, lessthan or equal to 10 wt %, less than or equal to 7.5 wt %, less than orequal to 5 wt %, less than or equal to 2 wt %, less than or equal to1.75 wt %, less than or equal to 2.5 wt %, less than or equal to 1.25 wt%, less than or equal to 1 wt %, less than or equal to 0.9 wt %, lessthan or equal to 0.8 wt %, less than or equal to 0.5 wt %, less than orequal to 0.2 wt %, or less than or equal to 0.1 wt % of the metalobject. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0 wt % and less than or equal to 17.5 wt%, greater than or equal to 0.8 wt % and less than or equal to 17.5 wt%, greater than or equal to 0.8 wt % and less than or equal to 1.1 wt %,or greater than or equal to 15 wt % and less than or equal to 17.5 wt%). Other ranges are also possible. The chromium content of a metalalloy may be determined by in accordance with ASTM E1086-08.

In some embodiments, a metal object comprises a metal alloy comprisingcarbon (e.g., an alloy comprising iron and carbon). Carbon may make upgreater than or equal to 0 wt %, greater than or equal to 0.01 wt %,greater than or equal to 0.02 wt %, greater than or equal to 0.03 wt %,greater than or equal to 0.05 wt %, greater than or equal to 0.07 wt %,greater than or equal to 0.1 wt %, greater than or equal to 0.15 wt %,greater than or equal to 0.2 wt %, greater than or equal to 0.25 wt %,greater than or equal to 0.3 wt %, greater than or equal to 0.35 wt %,greater than or equal to 0.38 wt %, or greater than or equal to 0.39 wt% of the metal object. Carbon may make up less than or equal to 0.4 wt%, less than or equal to 0.39 wt %, less than or equal to 0.38 wt %,less than or equal to 0.35 wt %, less than or equal to 0.3 wt %, lessthan or equal to 0.25 wt %, less than or equal to 0.2 wt %, less than orequal to 0.15 wt %, less than or equal to 0.1 wt %, less than or equalto 0.07 wt %, less than or equal to 0.05 wt %, less than or equal to0.03 wt %, less than or equal to 0.02 wt %, or less than or equal to0.01 wt % of the metal object. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 0 wt % and lessthan or equal to 0.4 wt %, greater than or equal to 0 wt % and less orequal to 0.07 wt %, or greater than or equal to 0.38 wt % and less thanor equal to 0.4 wt %). Other ranges are also possible. The carboncontent of a metal alloy may be determined in accordance with ASTME1086-08.

Further examples of elements that may be included in metal alloyssuitable for use in metal objects described herein include, but are notlimited to, aluminum (which may make up, e.g., greater than or equal to0.95 wt % and less than or equal to 1.30 wt % of the metal alloy), boron(which may make up, e.g., greater than or equal to 0.001 wt % and lessthan or equal to 0.003 wt % of the metal alloy), cobalt (which may makeup, e.g., greater than or equal to 0 wt % and less than or equal to 8 wt% of the metal alloy), copper (which may make up, e.g., greater than orequal to 0 wt % and less than or equal to 5 wt % of the metal alloy),manganese (which may make up, e.g., greater than or equal to 0 wt % andless than or equal to 12 wt % of the metal alloy), molybdenum (which maymake up, e.g., greater than or equal to 0.2 wt % and less than or equalto 5 wt % of the metal alloy), nickel (which may make up, e.g., greaterthan or equal to 2 wt % and less than or equal to 20 wt % of the metalalloy), phosphorus (which may be present in trace amounts and/or makeup, e.g., greater than or equal to 0 wt % and less than or equal to 0.05wt % of the metal alloy), silicon (which may make up, e.g., greater thanor equal to 0.2 wt % and less than or equal to 2 wt % of the metalalloy), vanadium (which may make up, e.g., greater than or equal to 0 wt% and less than or equal to 5 wt % of the metal alloy), tungsten (whichmay make up, e.g., greater than or equal to 0 wt % and less than orequal to 18 wt % of the metal alloy), and zirconium (which may make up,e.g., approximately 0.1 wt % of the metal alloy). The amount of each ofthe above-referenced elements in a metal alloy may be determined inaccordance with ASTM E1086-08.

For convenience, certain terms employed in the specification, examples,and appended claims are listed here. Definitions of specific functionalgroups and chemical terms are described in more detail below. Forpurposes of this invention, the chemical elements are identified inaccordance with the Periodic Table of the Elements, CAS version,Handbook of Chemistry and Physics, 75th Ed., inside cover, and specificfunctional groups are generally defined as described therein.Additionally, general principles of organic chemistry, as well asspecific functional moieties and reactivity, are described in OrganicChemistry, Thomas Sorrell, University Science Books, Sausalito: 1999.

The term “aliphatic,” as used herein, includes both saturated andunsaturated, nonaromatic, straight chain (i.e., unbranched), branched,acyclic, and cyclic (i.e., carbocyclic) hydrocarbons, which areoptionally substituted with one or more functional groups. As will beappreciated by one of ordinary skill in the art, “aliphatic” is intendedherein to include, but is not limited to, alkyl, alkenyl, alkynyl,cycloalkyl, cycloalkenyl, and cycloalkynyl moieties. Thus, as usedherein, the term “alkyl” includes straight, branched and cyclic alkylgroups. An analogous convention applies to other generic terms such as“alkenyl”, “alkynyl”, and the like. Furthermore, as used herein, theterms “alkyl”, “alkenyl”, “alkynyl”, and the like encompass bothsubstituted and unsubstituted groups. In certain embodiments, as usedherein, “aliphatic” is used to indicate those aliphatic groups (cyclic,acyclic, substituted, unsubstituted, branched or unbranched) having 1-20carbon atoms. Aliphatic group substituents include, but are not limitedto, any of the substituents described herein, that result in theformation of a stable moiety (e.g., aliphatic, alkyl, alkenyl, alkynyl,heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, oxo, imino,thiooxo, cyano, isocyano, amino, azido, nitro, hydroxyl, thiol, halo,aliphaticamino, heteroaliphaticamino, alkylamino, heteroalkylamino,arylamino, heteroarylamino, alkylaryl, arylalkyl, aliphaticoxy,heteroaliphaticoxy, alkyloxy, heteroalkyloxy, aryloxy, heteroaryloxy,aliphaticthioxy, heteroaliphaticthioxy, alkylthioxy, heteroalkylthioxy,arylthioxy, heteroarylthioxy, acyloxy, and the like, each of which mayor may not be further substituted).

The term “alkyl” refers to the radical of saturated aliphatic groups,including straight-chain alkyl groups, branched-chain alkyl groups,cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups, andcycloalkyl substituted alkyl groups. The alkyl groups may be optionallysubstituted, as described more fully below. Examples of alkyl groupsinclude, but are not limited to, methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, 2-ethylhexyl, cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, and the like. “Heteroalkyl” groups are alkylgroups wherein at least one atom is a heteroatom (e.g., oxygen, sulfur,nitrogen, phosphorus, etc.), with the remainder of the atoms beingcarbon atoms. Examples of heteroalkyl groups include, but are notlimited to, alkoxy, poly(ethylene glycol)-, alkyl-substituted amino,tetrahydrofuranyl, piperidinyl, morpholinyl, etc.

The terms “alkenyl” and “alkynyl” refer to unsaturated aliphatic groupsanalogous to the alkyl groups described above, but containing at leastone double or triple bond respectively. The “heteroalkenyl” and“heteroalkynyl” refer to alkenyl and alkynyl groups as described hereinin which one or more atoms is a heteroatom (e.g., oxygen, nitrogen,sulfur, and the like).

The term “aryl” refers to an aromatic carbocyclic group having a singlering (e.g., phenyl), multiple rings (e.g., biphenyl), or multiple fusedrings in which at least one is aromatic (e.g.,1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl), alloptionally substituted. “Heteroaryl” groups are aryl groups wherein atleast one ring atom in the aromatic ring is a heteroatom, with theremainder of the ring atoms being carbon atoms. Examples of heteroarylgroups include furanyl, thienyl, pyridyl, pyrrolyl, N lower alkylpyrrolyl, pyridyl N oxide, pyrimidyl, pyrazinyl, imidazolyl, indolyl andthe like, all optionally substituted.

The terms “amine” and “amino” refer to both unsubstituted andsubstituted amines, e.g., a moiety that can be represented by thegeneral formula: N(R′)(R″)(R′″) wherein R′, R″, and R′″ eachindependently represent a group permitted by the rules of valence.

The terms “acyl,” “carboxyl group,” or “carbonyl group” are recognizedin the art and can include such moieties as can be represented by thegeneral formula:

wherein W is H, OH, O-alkyl, O-alkenyl, or a salt thereof. Where W isO-alkyl, the formula represents an “ester.” Where W is OH, the formularepresents a “carboxylic acid.” In general, where the oxygen atom of theabove formula is replaced by sulfur, the formula represents a“thiolcarbonyl” group. Where W is a S-alkyl, the formula represents a“thiolester.” Where W is SH, the formula represents a “thiolcarboxylicacid.” On the other hand, where W is alkyl, the above formula representsa “ketone” group. Where W is hydrogen, the above formula represents an“aldehyde” group.

As used herein, the term “heteroaromatic” or “heteroaryl” means amonocyclic or polycyclic heteroaromatic ring (or radical thereof)comprising carbon atom ring members and one or more heteroatom ringmembers (such as, for example, oxygen, sulfur or nitrogen). Typically,the heteroaromatic ring has from 5 to about 14 ring members in which atleast 1 ring member is a heteroatom selected from oxygen, sulfur, andnitrogen. In another embodiment, the heteroaromatic ring is a 5 or 6membered ring and may contain from 1 to about 4 heteroatoms. In anotherembodiment, the heteroaromatic ring system has a 7 to 14 ring membersand may contain from 1 to about 7 heteroatoms. Representativeheteroaryls include pyridyl, furyl, thienyl, pyrrolyl, oxazolyl,imidazolyl, indolizinyl, thiazolyl, isoxazolyl, pyrazolyl, isothiazolyl,pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, triazolyl, pyridinyl,thiadiazolyl, pyrazinyl, quinolyl, isoquinolyl, indazolyl, benzoxazolyl,benzofuryl, benzothiazolyl, indolizinyl, imidazopyridinyl, isothiazolyl,tetrazolyl, benzimidazolyl, benzoxazolyl, benzothiazolyl,benzothiadiazolyl, benzoxadiazolyl, carbazolyl, indolyl,tetrahydroindolyl, azaindolyl, imidazopyridyl, qunizaolinyl, purinyl,pyrrolo[2,3]pyrimidyl, pyrazolo[3,4]pyrimidyl, benzo(b)thienyl, and thelike. These heteroaryl groups may be optionally substituted with one ormore substituents.

The term “substituted” is contemplated to include all permissiblesubstituents of organic compounds, “permissible” being in the context ofthe chemical rules of valence known to those of ordinary skill in theart. In some cases, “substituted” may generally refer to replacement ofa hydrogen with a substituent as described herein. However,“substituted,” as used herein, does not encompass replacement and/oralteration of a key functional group by which a molecule is identified,e.g., such that the “substituted” functional group becomes, throughsubstitution, a different functional group. For example, a “substitutedphenyl” must still comprise the phenyl moiety and cannot be modified bysubstitution, in this definition, to become, e.g., a heteroaryl groupsuch as pyridine. In a broad aspect, the permissible substituentsinclude acyclic and cyclic, branched and unbranched, carbocyclic andheterocyclic, aromatic and nonaromatic substituents of organiccompounds. Illustrative substituents include, for example, thosedescribed herein. The permissible substituents can be one or more andthe same or different for appropriate organic compounds. For purposes ofthis invention, the heteroatoms such as nitrogen may have hydrogensubstituents and/or any permissible substituents of organic compoundsdescribed herein which satisfy the valencies of the heteroatoms. Thisinvention is not intended to be limited in any manner by the permissiblesubstituents of organic compounds.

Examples of substituents include, but are not limited to, alkyl, aryl,aralkyl, cyclic alkyl, heterocycloalkyl, hydroxy, alkoxy, aryloxy,perhaloalkoxy, aralkoxy, heteroaryl, heteroaryloxy, heteroarylalkyl,heteroaralkoxy, azido, amino, halogen, alkylthio, oxo, acyl, acylalkyl,carboxy esters, carboxyl, carboxamido, nitro, acyloxy, aminoalkyl,alkylaminoaryl, alkylaryl, alkylaminoalkyl, alkoxyaryl, arylamino,aralkylamino, alkylsulfonyl, carboxamidoalkylaryl, carboxamidoaryl,hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxy, aminocarboxamidoalkyl,alkoxyalkyl, perhaloalkyl, arylalkyloxyalkyl, and the like.

Example 1

This Example describes the preparation of four binder compositions andthe formation of metal-based composite structures therefrom.

Four binder compositions having the components shown in Table 1 wereeach prepared by the procedure described below. First, the componentsfor the binder composition other than the concentrated solution ofammonium hydroxide were charged into a flask. For binder compositions 2and 3, the concentrated solution of ammonium hydroxide was then added insufficient amount to cause the mixture to reach the desired pH. Next,for all binder compositions, the resultant mixture was magneticallystirred at room temperature for 1 hour. Finally, the homogeneoussolutions were filtered through a Buchner funnel. After these steps,binder composition 1 had a pH of 2.1.

TABLE 1 Binder composition no. 1 2 3 4 (comparative) Amount of 50 wt %aqueous solution 900 g 180 g 180 g of poly(acrylic acid) with M_(w) = 4kDa (Sokalan CP10S; purchased from BASF Inc.) Amount of Poval 3-98(polyvinyl 5 g alcohol) Amount of glycerol (purchased 50 g 10 g 10 gfrom Sigma-Aldrich, Inc.) Amount of isopropanol (purchased 250 g 50 g 50g from Sigma-Aldrich, Inc.) Amount of Thetawet FS-8150 2.5 g 0.5 g 0.5 g0.1 g (purchased from ICT, Inc.) Amount of deionized water 1297.5 g 259g 259 g 95 g Amount of concentrated solution Sufficient to bring pH ofSufficient to bring pH of of ammonium hydroxide in water bindercomposition to 6.3 binder composition to 7.5

For binder compositions 2-4, metal-based composite structures wereproduced from a mixture thereof with a metal powder comprising a 4140low alloy steel particles having a D90 of approximately 25 microns. 190g of the 4140 low alloy steel powder and 36 g of the relevant bindercomposition were charged into a mixing cup of a Flack Tech Speed Mixer.The cup was then spun at approximately 800 rpm under 20 mmHg of vacuumfor 2 minutes, which yielded an even, bubble-free suspension. Next, thebubble-free suspension was poured into five molds. The filled molds wereallowed to sit for 2 hours, after which the supernatant liquid wasremoved from the settled 4140 low alloy steel powder by pipette. Then,the filled molds were allowed to dry at 35° C. in an oven under nitrogenat atmospheric pressure for 24 hours. After drying, the oven was heldunder nitrogen and subject to the following temperature profile: (1)heating to 105° C. at 0.67° C./minute; (2) holding at 105° C. for atleast 1 hour; (3) heating to 190° C. at 1.1° C./minute; (4) holding at190° C. for 1 hour. Then, the heating element of the oven was turnedoff, and the oven was held under nitrogen and allowed to cool to roomtemperature.

An attempt was made to fabricate metal-based composite structures frombinder composition 1 and the 4140 low alloy steel metal powder describedabove by the procedure described above. However, approximately 1 hourafter the relevant even, bubble-free suspension was poured into themolds, it began to show strong gas evolution. This was believed toindicate a lack of compatibility with the 4140 low alloy steel, and sothe attempt was abandoned.

After the molds comprising the metal-based composite structure formedfrom binder compositions 2 and 3 reached room temperature, a portionthereof were demolded and then broken to expose their cross-sections.The cross-section of the metal-based composite structure prepared frombinder composition 2 had voids, while the cross-section of the brownpart prepared from binder composition 3 lacked voids. As voids aretypically considered undesirable, it is believed that bindercompositions having a pH in excess of 6.3 are desirable for thepreparation of metal-based composite structures from 4140 low alloysteel powders.

Another portion of the metal-based composite structures formed frombinder composition 2 and those formed from binder composition 4 weredemolded and then sanded with 220 grit sandpaper. After sanding, themetal-based composite structures had smooth, even surfaces and lackedsharp edges at their corners. The average transverse flexural strengthsof the these sanded bars was measured in accordance with ASTM B528-16.The average transverse flexural strength was determined to be 11 MPa forthe sanded bars formed from binder composition 3 and 4 MPa for thoseformed from binder composition 4. Accordingly, binder composition 3,which included a low molecular weight polymer comprising an acrylic acidrepeat group, performed better than binder composition 4, which did not.

Example 2

This Example describes the preparation of three binder compositions andtheir use in binder jetting.

Three binder compositions having the components shown in Table 2 wereeach prepared using the method described in Example 1.

TABLE 2 Binder composition no. 5 6 7 Wt % poly(acrylic acid) 15.94 19.3320 with M_(w) = 4 kDa Wt % isopropanol 9 10 Wt % Thetawet FS-8150 0.090.1 Wt % glycerol 1.8 2.04 2 Wt % pH ammonium hydroxide 10.5 13.071,2,-hexanediol 2.15 Wt % deionzed water Balance Balance Balance

For each binder composition shown in Table 2, droplets were producedusing a Samba G3L ink-jet print head equipped with Megnajet CIMS-2HFR(available from Megnajet, Northamptonshire, England) recirculationsystem. Droplet volume and velocity were determined using a stroboscope,a camera, and imaging software, all available from JetXpert, Nashua,N.H., USA. For each binder formulation, ink-jet pulse voltage, pulsetime, and pulse sequence were adjusted to produce droplets havingvolumes in the range of 9 pL to 12 pL and velocities in range of 8 m/secto 12 m/sec when measured at 0.5 mm from the print head nozzle at 24 kHzpulse frequency. If more than 1 droplet was produced for each pulsesequence, the pulse sequence was adjusted to cause the droplets tocoalesce into a single droplet not farther than 0.5 mm from the printhead nozzle. The resulting pulse sequence is referred to herein as “thelarge drop waveform”. Latency was assessed by operating the print headat the large droplet waveform until stable droplet formation wasestablished, turning off the print head for 5 sec, turning the printhead back on again, and then determining how many droplets were ejectedfrom the print head before stable droplet formation was reestablished.

Table 3 lists the pH of each binder composition and the average numberof droplets ejected from the print head prior to resumption of normalprinting for each binder composition.

TABLE 3 Binder Latency (average number of droplets composition ejectedfrom the print head prior no. pH to resumption of normal printing) 5 714 6 7 39 7 3 399

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,and/or methods, if such features, systems, articles, materials, and/ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

What is claimed is:
 1. A method of additive manufacturing a metal-basedcomposite structure by binder jet printing, the method comprising:depositing a first layer of metal powder; depositing a bindercomposition on at least a portion of the first layer of metal powder,the binder composition comprising water and a low molecular weightpolymer including an acrylic acid repeat unit, wherein the bindercomposition has a pH of greater than or equal to 4; and drying and/orcross-linking at least the binder composition deposited on the firstlayer of the metal powder, thereby forming a metal-based compositestructure.
 2. (canceled)
 3. The method of claim 1, wherein the lowmolecular weight polymer has a weight average molecular weight of lessthan or equal to 40 kDa. 4-10. (canceled)
 11. The method of claim 1,wherein the binder composition further comprises an adhesion promoter.12. The method of claim 11 wherein the adhesion promoter comprises afunctional group capable of binding to the metal powder.
 13. The methodof claim 12, wherein the functional group capable of binding to themetal powder is a sulfur-containing functional group.
 14. The method ofclaim 13, wherein the sulfur-containing functional group comprises athiol.
 15. The method of claim 12, wherein the functional group capableof binding to the metal powder is a first functional group, and theadhesion promoter further comprises a second functional group.
 16. Themethod of claim 15, wherein the second functional group is anucleophilic functional group or an electrophilic group.
 17. The methodof claim 15, wherein the adhesion promoter further comprises a thirdfunctional group.
 18. The method of claim 17, wherein the thirdfunctional group is a nucleophilic group or an electrophilic group. 19.The method of claim 11, wherein the adhesion promoter is or comprisescysteine, cystine, methionine, homocysteine, an amine thiol,dithiothreitol, mercaptoethanol, a thiocarboxylic acid, and/or athiocarboxylate. 20-26. (canceled)
 27. The method of claim 1, whereinthe metal powder comprises gold metal and/or a gold alloy. 28-71.(canceled)
 72. A binder composition for additive manufacturing of metalobjects by binder jetting, the binder composition comprising: water; alow molecular weight polymer including an acrylic acid repeat unit; across-linking agent comprising a polyol, a multifunctional amine, and/ora multifunctional thiol; and a pH modifier. 73-77. (canceled)
 78. Thebinder composition of claim 72, wherein the binder composition furthercomprises an adhesion promoter.
 79. The binder composition of claim 78,wherein the adhesion promoter comprises a functional group capable ofbinding to a metal powder.
 80. The binder composition of claim 79,wherein the functional group capable of binding to a metal powder is asulfur-containing functional group. 81-116. (canceled)
 117. Ametal-based composite structure formed by additive manufacturing, themetal-based composite structure comprising: a metal powder, wherein thewt % of the metal powder in the metal-based composite structure isbetween 92 wt % and 99.9 wt %; and a binder, wherein the bindercomprises a low molecular weight polymer including an acrylic acidrepeat unit. 118-130. (canceled)
 131. The metal-based compositestructure formed by additive manufacturing of claim 117, wherein thebinder composition further comprises an adhesion promoter.
 132. Themetal-based composite structure formed by additive manufacturing ofclaim 131, wherein the adhesion promoter comprises a functional groupcapable of binding to the metal powder.
 133. The metal-based compositestructure formed by additive manufacturing of claim 132, wherein thefunctional group capable of binding to the metal powder is asulfur-containing functional group. 134-141. (canceled)